I'm trying a new recipe today. If I like it I will being freezing the rest of the cupcakes till Wednesday and deliver them Thursday. Can I make peanutbutter b/c and it still be good in my fridge till thursday? should i freeze it? Or just make enough to try for today?

I'd freeze it if I'm not going to use it within 48 hours.

Here's a thread with more info on BC.
http://www.cakecentral.com/cake-decorating-ftopict-1353.html

Well, I suspect you'll find many who would just leave it sitting on the counter. Buttercream does fine. However, for that length of time, I would likely just put it in the fridge. If it were longer than a week, I'd freeze. Either way, you'll need to take it out a while before you need it to let it soften up.