Please help me plan a dinner for 25 strangers?

You do have a lot of wonderful recommendations! I agree with garlic@lemon. When I entertain for my women friends, we want to eat healthy, have great beverages and be able to move around and talk to one another. We are also uncomfortable if we can't help in the kitchen, set-up, clean-up. We don't one one person stuck in the kitchen doing everything.
Also when it is just us 'girls' together, we want informal not formal.

Will you have servers or is this just you doing it alone? What is the group expecting? What is the purpose of the gathering? The answers to these questions might also illuminate your menu. Let us know how it turns out!

lloreen - you have lots of great suggestions! My answer was based on the main course being eaten at tables. We found that choices were the most important factor. With 25 people, count on someone spilling something, plan your menu accordingly, and practice your equanimity.
@sexyLAMBCHOPx - yeah, my answer could be seen that way. My friend and I (both feminists who love to eat) looked at our data (all the leftovers 3 years running) and decided that these women were more health conscious - that is, they ate their main meal at lunch. Also, we asked them and that is what they said. That way, we could get around our own ideas about women's rights to a hearty appetite and make food that would delight and be eaten by the end of the evening.

On another thread here, someone recently mentioned this contest, "Your Best One Bite Party Snack." You might find some good ideas there too.
https://food52.com/contests/265-your-best-one-bite-party-snack

another idea for choice at a buffet - a pancake or waffle bar with toppings including meat, vegetables, nuts, cream, fruit etc. Think crepes, potato pancakes, whole wheat waffle, dollar-size pancakes etc. Another way to allow for allergies, appetites, end of day energy or lack thereof.

Did this for my coworkers a few years ago and I set up a salad and soup bar. Prep and bag your veggies (don't buy salad mix), make up some salad dressings, offer nuts, hard boiled eggs, cheeses, marinaded veggies. Keep things fresh, interesting and with a crock pot soup and some crusty bread, everyone can have something they are happy with. Other option is to set out a tapa style repast. Breads, cheeses, olives, roasted peppers, and meats are nice for everyone.

Something like a frittata or quiche would be great. Can be eaten with fingers. It's nice to pre-slice so that people don't get tangled up with knives and spatulas.

p.s. For a group that big: it might be helpful to put at least one trash can somewhere near your kitchen, other than the main can in your kitchen, so people can tidy up without a traffic jam in your kitchen. I actually go so far as to dispose of a fake dirty plate in my additional trash can so people can see "yes, this is a garbage can" without having to wander around asking.

With large groups where I'm unsure or eating habits, I like make your owns... Make your own salad, lots of toppings to choose from and lots of dressings. Make flat bread dough. Lots of toppings. They cook in about 10 minutes. Fun interactive dinner.

It'll be a knees up situation - my table doesn't seat 25 ;) I'd love to do soup, but it'd be treacherous to balance.
I like the Indian curry suggestion....I had been considering butter chicken with rice and some veggies...

Curry!
Curry is awesome, you can make vegetarian, vegan, meat, or better still a selection. Mild, you won't even know it's curry, to burn your taste buds off hot. Best of all, CURRY TASTES BETTER WHEN MADE THE DAY BEFORE. So you can get all your curry making chores done the day before, then make rice, cut up nan, and if you are feeling brave, fry up some popads.

My personal favourite oh-my-goodness,-I'm-cooking-for-boatloads-of-people-I-have-no-idea-their-dietary-preferences-menu looks like this:

- Very mild curry made from onions, chickpeas, and pataks mild curry paste. Maybe some tomatoes, maybe not. Fry onions, combine the rest, add water as needed, cook an hour or so.
-Spicy vegetarian curry like Aloo Gobi (easily made vegan)
-All the stuff in the back of my fridge extra spicy curry - which often has leftover roast beast (bones removed), loads of curry paste, onions, potatoes, lentils and other pulses, carrots... what have you.
-One spicy vegetable and pulse curry, probably vegan just in case.

At least one of each, meat, vegan, vegetarian, mild and spicy. Write up some labels of what's in it (including the make of curry paste if you didn't make your own - huge difference in dietary needs). Not all curry paste is vegan friendly!!! Pataks contains the fewest allergens and many of their curry pastes are soy free, animal free, nut free (but possible traces), &c. Jamie Oliver's book Food Revolution has some Kick-arse recipes for home made curry pastes, really easy ones with very few, readily available ingredients.

Make the curries the day(s) before, and reheated in slow cooker, oven, stove, whatever's available. I like oven best if you have enough pots for that.

Chutneys, also best made the day(s) before, or from a jar.

Salad is a great idea, with add-your-own dressing (lots of dietary problems with pre-dressed salad), as well as a bottle of olive oil and a bottle of balsamic for those of us who are super-sensitive to standard dressing ingredients (ie, vegans don't eat honey, mustard can contain bad things... &c).

I think papads are gluten free, but in case they aren't (or someone has issues with traces of gluten) I put some rice crackers out with some hummus (also made the day before, also vegan friendly).

Set it up like an Indian restaurant buffet, and sit back and watch them dig in.

Best of all, with curry you don't have to worry about getting the timing right for the different dishes, or carving the beast, or all those worrisome little details. Just heat and serve.

Will you have table seating for this group or is it a knees-up on chairs and sofas, etc.?

For several years, a friend and I cooked a celebration/thank-you dinner in January for about 25 women who volunteered for our non-profit. We discovered: 1) When we made hearty main dishes (e.g. coq au vin or other heavy mains) we had lots left over. After about 4 years, we ditched the main dish altogether. 2) Appetizers are good. Offering variety of small bites when they arrived was popular and allowed us to make almost everything ahead of time. This was accompanied by champagne, wine, and fruit coolers. 3) Women and salads go well together. We made two different salads and let folks choose. 4) Soups were popular. You can make two different soups. That way, you can allow for food allergies. Be sure to send out the email and ask folks to tell you what the allergies are. Add good bread or crackers and either cheese or hummus or both. 5) Dessert, while well-liked, also needed to be something that women could take smaller portions of. Again, we made tiny, decorated cupcakes in a couple of flavors, and something else. One year I made small home made oreos as well; another year when I was not feeling well, I made a couple of apple crisps and maple whipped cream and allowed everyone to serve themselves. Mousse in small cups, a variety of cookies in smaller sizes and other small bites helps you to prepare ahead of time and keeps leftovers down. Most of the women ate their main meal at lunch and preferred to eat lighter at dinner - or maybe it was the perceived peer pressure around other women. Whatever the reason, the above advice helped us to have very successful dinners. Use or borrow beautiful serving pieces, have flowers and candles, and use as much real china, glasses, and cups as you can handle. If that is not possible, use the highest quality disposables you can afford. Bribe one or more of your friends to help you on the night of the party.

I like to do a tostada bar for large groups of people. It's fun and let's everyone make their tostada to suit their taste. Plus, you can pretty much prep everything in advance.