It's your party, and you'll plan if you want to.

Sorry for the pun.

You can do whatever is best for all concerned. Providing the meat is
probably fine.
If you're planning the details for an undisclosed number of guests, it might
be best to throw a "we're thinking of having a party...would you attend?"
hypothetical out in the air.
Might even get some of the locals to offer to do spill-over cooking should
more arrive than expected.

If you have no clue who is coming, have them phone you. Without a head
count, could be a disaster should much more arrive than prepared for.
Having them call ahead to confirm is wise.

Also, as you can't always rely on the arrivals to prepare a good portion,
might also be a good idea to prepare a side or three yourself, just in case.