dinner party for 10 or 12, dishes that heat up well?

Since you dinner is fall themed, I would also throw a bottle of apple cider in a pan or the crockpot with some cinnamon, oranges, cloves and other mulling spices and let that simmer away. Or if you are more of a wine person, you could make mulled wine.
Also a couple great, easy fall desserts are apple or pear crisp and baked apples.

I'm having a dinner party for 12 this weekend and am making either of these go-to recipes that couldn't be more dependable, flavor-wise. In both cases, the flavor improves when made 2 days (!!!) in advance and reheated. I've made both several times to rave reviews, and Ina Garten and Daniel Boulud wouldn't lead you (and have never led me) astray;-). A lovely salad and hunk of bread and you're freed up to worry about atmosphere instead of kitchen duty. http://www.foodnetwork.com/recipes/ina-garten/beef-bourguignon-recipe.html
http://www.epicurious.com/recipes/food/views/Shortcut-Pork-Cassoulet-5880

Endorse replacing the steak (stress for a big group) with roasted meat. Haven't read all your recipes so pls forgive if I double-up on something already suggested, but BRAISED meats heat up beutifully and taste even better after some day(s) to let flavors blend. Classic brisket, boeuf bourgignon, chicken tagine, Persian chicken recipes (with walnut & pomegranate), Arabic chicken recipes (with loads of sliced simmered onions), crown roast of lamb (for indulgence and celebration). For other rich touches - a salad with nuts and good dried fruit, a frozen dessert (lemon cake, parfait), a boozy trifle, or - for dessert or last course - aged Parmesan with vin santo or Port to drink on the side. Good luck and let us know how it goes ;) (NOT the same as Vonnegut's phrase).

I can't reply to your reply so here is a new post for your questions to me.

-about the steak, you could do a thick steak, sear and hold aside to finish in the oven like a restaurant would do yes. Any cut 1-1/4 inch to 2 inches thick. But you still are dealing with checking when the steak is done. It will need to rest 8 minutes, then be sliced. For reheating meat, you will usually want to go with a completely cooked piece like a stew or braise. But it seems like you are trying to do something more interesting. I do think a great short rib dish is not a usual everyday dish and can be done the day ahead and even improves. That will go with carrot soup or roasted veggies too. I like short ribs in wine.

More ideas:
My 'go to' easy elegant dinner party dish is really simple but as impressive as a restaurant dish--it IS a restaurant dish. Salmon with Thai Curry Sauce. It is assembled as a tower with a scoop of Basmati (or Jasmine) rice on the bottom, Then the salmon, some sauce drizzled around the plate and topped with an Asian Slaw. If you know how to roast salmon, do it without flavorings as you can cook the salmon any way. The rice is done easiest in a rice cooker, but the oven is foolproof and will hold it on low, or stovetop is fine of course. Do the sauce a day ahead and reheat gently. (Leftovers work on beef, chicken or veggies too.) Add the curry paste more or less to taste for hotness. Triple the sauce for 10 to 12, very simple to make in one pot. If you think anyone will want less sauce, just dot it around the plate and pass separately, some people will like more. Cut and bag the finely shredded napa cabbage up to a day ahead. Just add the cucumber, mint and cilantro an hour before guests arrive (gently tear the mint so as not to blacken it.) Then toss with the soy and vinegar just before serving. Have someone help you assemble: rice, salmon, sauce, slaw, peanut topping (or toasted sesame seeds work) (my sister helped me last and formed the rice is a ramekin and turned it onto the plate.) That's a one dish meal. If you wanted to start with a small cup of carrot soup you could, flavor with ginger. But not needed. Keep before dinner nibbles simple. I'd serve some cashews (seasoned like Trader Joe's thai ones), and seasoned edamame, for instance. Maybe add an Asian flavors seasoned tofu dip with crackers. I don't see the burrata working here. Something like deviled eggs topped with tobiko, caviar or salmon roe. Even a purchased liver pate. This is sooo easy, just make yourself a timeline.
http://www.terrarestaurant.com/pdf/salmon_thai_curry.pdf

A more rustic dish but one that can be doubled, made the day before and reheats well is a great chicken and sausage rice dish from Fine Cooking. See the pic this is very pretty (I use red bell pepper) with deep flavors. You could use boneless thighs for easier eating (I have done it and even cut them up and larger chunks of breast) and in that case you would use chicken broth for all or part of the water. Make 3 batches, everyone likes extra sausage. Cook each separately if you like, leave the rice on the moist side, and combine in a large roasting pan, cover with foil and chill. You can reheat gently in the 300F oven for 45 minutes. I often toss frozen peas on during the last 10 minutes for color and freshness. Now you can have a nice salad or whatever Mediterranean or Spanish flavors to add. The cup of carrot soup works too. Any citrus fruit in salad or dessert is nice. Grapefruit and avocado salad with bibb lettuce would be great. Your burrata with fruit should work. I often serve with Molly Katzen's Orange and Radish Salad. The lemon cake mentioned with be perfect, maybe even with a scoop of sorbet.
http://www.finecooking.com/recipes/arroz_con_pollo.aspx

http://www.globalgourmet.com/food/special/2000/katzen/salad.html
http://www.molliekatzen.com/recipes/recipe.php?recipe=beet_fennel_salad

Even if you don't use it this time, these are two fantastic pretty simple dishes I've made again and again if you want to expand your repertoire.

Add indulgence with a dessert, maybe purchased, but know that most cakes improve overnight if wrapped airtight.

Roasted carrot soup sounds really wonderful, very seasonal. If you added some crusty bread or croutons you could cut back on the portions size for the main course. I think the suggestion of short ribs is brilliant and more forgiving than steak. I think you have a good plan now so good luck with your trial run!

Heather,
Tacos would be great! Anything where people can assemble the food themselves is fun and breaks with expectation. But if you want to keep a fall flavor maybe something like a beef stew with mashed potatoes (or you can kick it up a notch and make beef stroganoff which isn't as difficult as you might think......basically good beef with mushroom, some wine and cream), chili with baked potatoes, lasagna, mac and cheese, pork tenderloins http://www.barefootcontessa.com/recipes.aspx?RecipeID=114&S=0 . Depending on how much time you have to prepare (are you at work all day the day of, etc.) I don't think it is cheating to buy parts of the meal prepared - pre-cooked chickens, etc. and make them yours. Just keep it simple.
You might want to look at Ina Garten's cookbooks. Her whole philosophy is not to fuss and have the food taste good. I haven't met a recipe of hers that wasn't foolproof and delicious and she has great menu ideas. Also, why not think in terms of separate dishes? Maybe serve a soup and then have a lighter (warmer weather) meal, Mediterranean style. Just choose what you are comfortable preparing so you enjoy the evening, which in turn will pass to your guests.
BTW I write all this with a vast amount of experience to draw upon, being over ambitious and determined: the meal one of the vegetarian courses was found 2 days later in the oven: the turkey cooked with giblets (on 2 occasions); the duck and blackberry sauce that set fire to the oven and more. Great memories, but stressful!!! So, go simple and enjoy your dinner party. And don't forget to do a backward timeline, to aid in the timing.

The most important thing with the whole meal is that you provide your guests with a great evening of food and company (including you!) and you don't end up frazzled in the process (either from exhaustion or nerves). I think your menu looks good but looks a little labor intensive if you are planning to do everything yourself, even doing it in advance. I would change the steak (for all the reasons nutcakes stated) and possibly simplify what you are making. I am also not sure if I would make roasted vegetables as they can overcook. Get a guest to bring dessert, or do ice cream with hot chocolate sauce or lots of toppings to make sundaes. Do things as simply as possible so you enjoy yourself.

You can't cook the steak to the correct temp and then reheat it or it will be overcooked and dry. It would be better to do it an hour ahead and serve it at room temp. I personally have not seared steak and then finished it later and I would hesitate to try it on guests without testing. I'm really doubtful of that working well on a flank steak because it is practically done after a sear anyway. I think it would finish cooking as it rests, making it possibly overcooked if you try to heat it up again.

sounds like a great menu!
I would also serve some decent bread or roast potato wedges along with the other vegetables for a starchy side; mashed potatoes might also be very nice.
And for dessert: just ask one of your guests to bring it, usually there is someone who loves baking and just helping in general!

Heather, I think that a "starch" is missing. I would add something like rice pilaf or orzo (i.e., drizzled with olive oil and some parmesan) or even a nice baked macaroni and cheese dish. Either of these 3 dishes can be prepared in advance. For the mac and cheese , you could prepare it the day before and bake it maybe one hour before your guests arrive. But this is just me because I am a "starchy" type of girl. LOL

Check out this flank steak recipe, its one of my favorites on this site. It is amazing served at room temperature or warm up in a low oven. I have used skirt steak more than flank with great results. You could deconstruct the recipe entrée. https://food52.com/recipes/13349-flank-steak-on-texas-toast-with-chimichurri

I think your menu sounds perfect. Is there any way that person who is going to help clear could come and cook the steak for you so you could relax? If not, Abbie's idea of testing a small steak is a good one.

Heather your menu sounds very good - I would suggest a test for the steaks - do a small one, sear and then rest and see if it's OK finishing in the oven (make sure it doesn't dry out or overcook) in theory it sounds fine though! It can be finishing as soon as the veggies are done. I do the buratta / peach thing too, but you probably can't get very good peaches any more - what about switching to plums or pears? Down here the pears are excellent right now. Between a leafy salad and whatever fruit you land on, plus the buratta,it sounds like you have fresh and indulgent covered! Not sure if you have put and thought into dessert - you are already doing a lot, so think about a purchased dessert or one that you can make ahead. I have made this lemon cake several times - it's fine a day ahead and SO good:

https://food52.com/recipes/8867-pearl-s-lemon-olive-oil-cake