Colones?
 

we are staying entirely in resorts and probably won't do any exploring on our own so am assuming I will only need colones for tips. How much would you withdraw for 10 days?

You don't really need to exchange your money if you're staying entirely in resorts. We've taken over ten trips and dollars have been accepted everywhere that we've gone, especially if you're staying in tourist areas/resorts. Some places won't accept anything over a twenty dollar bill.