Given the update on the size of the house and the preference for casual - I'd go for a selection of sandwiches from Subway, too.
I completely agree, so long as your picking up the sandwiches the day of, not the day before.
It sounds like a more casual affair where the need is to feed people "something" before they go off to other functions. I think Subway is a perfect menu plan for this. It's not overly filling, but it satisfies the need to eat.
I suggest that you contact your local Subway, several days in advance
, and ask them what their recommendations are. In my experience (I've ordered large food menus from them twice) they are pretty good with their calculations as to how much food for the age group/party style that you need.
Ask them about their sandwich trays (usually 3-inch subs) and the price difference from ordering several foot-long subs. I'm thinking that a variety of 3-inch subs is the way to go.
Ask them about the freshness of the sandwiches . . . how far in advance will the sandwiches be made prior to your pick-up time.
I say calling them several days in advance is a wise/kindness move just so that the restaurant has a heads-up on a large order, especially since it's a "holiday."
With your guests, I don't think that I would take orders for what they want to eat. I think that a variety of your choosing (a few veggie, beef, turkey, etc.) should please everyone.
Maybe add some salads (potato, coleslaw, pasta salad, picked up the day before) and some chips (from Subway) and you're good to go!
Good luck! Please let us know how your party went.