Place cards and guests

I'm not sure what the appropriate way to fill in the place cards are regarding guests.

If you know the guest's name, they get their own place card right? And if you don't know the name, you write Mr. John Smith & Guest?

Do husband and wife get one place card?

I think I'll be doing

Mr. on one Mrs. on the other

Then... 'so and so' on the other... well.. try to get the guests name or write 'guest' maybe leave it blank?

For couples we are using 1 place card

Mr & Ms. with both names if not married yet

For singles they get their own card and since we are not giving anyone a +1 if we were I would do

Mr. XXX and gues (if I couldn't find out the name)