The game is coming along well. Does anyone have a good idea about how many coins / cost values is a good amount? Do people like small or large numbers more?

Depends on the context. Are the coins being used for some kind of score, or are they used as currency?

Either works as long as you're being consistent, but if you're doing something arcade-y I think multiples of 5 and 10 or 50 and 100 are traditional.