Sandwich suggestions

I second the bahn mi suggestion! I would also add middle eastern style pita wraps, I make these in advance for big crowds in the summer and they always go over a treat -- shawarma chicken, rice pilaf, humos, cucumber and tomato salad for one, and grilled or roasted veggies (some combo of peppers, onions, eggplant, carrot, squash, sweet potato, potato) with humos, rice pilaf, and cucumber and tomato salad -- you get the idea! maybe also look into muffelata (sp?) type sandwiches? They definitely hold up as well

For the vegetarians, I have a suggestion. These are sandwiches that are very popular in my home country Haiti. You take canned asparagus, drained them, and make a paste with the asparagus, mayonnaise, salt (if necessary), a bit of paprika, garlic powder, and/or any other spices of your liking. Spread them on white bread (with the crust removed) and cut into 2/4 triangles or squares. My mom herself, but this takes more time to do, is to roll each slice of white bread until they are flat, she then spreads seasoned mayo on the bread and place 1 or 2 asparagus. She rolls the bread and cuts it into 2 or 3 portions. Repeat again.

It's summer which always makes me think, "picnic." What if you made a pimento cheese spread (like the one on this website) and topped it with thick slices of tomato for the vegetarian option? The juices from the tomato would soak into the baguette beautifully. You could also make pan bagnat (https://food52.com/recipes/6896-pan-bagnat-le-french-tuna-salad-sandwich) if your guests are okay with fish. It will only get better if you make it ahead of time.

Bahn mi are easy to make in quantity, and work well made in the whole-baguette format you are thinking of. The daikon/carrot pickles, green chiles, cucumber, mayonnaise, and herbs would go on all the sandwiches, and then fried tofu and/or sauteed mushrooms (or if you don't want to make it yourself, purchase smoked tofu or some other seasoned tofu) for the vegetarian ones, and meat of your choice for the non-vegetarian ones. If you want them to be vegan (and not worry about room temp raw egg), some of the vegan mayonnaise out there is very good, and would indistinguishable from egg mayonnaise in a seasoned context like bahn mi.
There are tons of places to get instructions for bahn mi, but here's a good place to start: http://www.vietworldkitchen.com/blog/2009/06/banh-mi-sandwich-recipe.html

Vegetarians( not Vegans) will eat cheese so you could make a nice fresh mozzarella and tomato hero with some wilted spinach on top and a little balsamic dressing on it. You can add prosciutto if you want to some of them. For the meat lovers try a ham / salami and provolone combo , some chopped lettuce and a classic red wine vinegar & olive oil dressing. If you are feeling bolder, grill some sausages, top with fresh ricotta and some balsamic sauteed shallots . Lastly , some grilled chicken ( you can buy it already grilled if you want) with wilted spinach or broccoli rabe , brush the bread with a good brand of vodka sauce. I like to use different breads too make it more interesting. Good luck.

One fun idea...make a selection of pesto sandwiches, using the classic Genoese and others (Red/rosso from Sicily for the vegetarians has almond tomato olives spices; Trapanese also from Sicily is similar but also has anchovy caper & peppers). See Saveur magazine Aug 2011 article and other sources for recipes. One or more could have added chicken or other meat to taste.