When I go to NYC I just get the 7 day pass which will cost $33 - $32 for the pass and $1 for the card
It will be a lot less hassle than trying to work out how often you might use it and worrying about having a balance on it in case you go over your estimate.
Yes you can use the pay per ride for more than one person but again you'll have to work out how many trips that will be for and ensuring you have enough credit on it. And what if your group splits up? They will soon need their own pass anyway!
This table on the MTA website might help
http://web.mta.info/nyct/fare/FaresatAGlance.htm#save