How many credits do I need?
It depends on what college you're in, but for CAS you need 120 total in order to graduate, with at least 100 being from within CAS itself.
How much is "much" for one semester?
First-semester freshman are not allowed to take more than 18 so that they don't overwhelm themselves, and I think that's probably a good number to go with. Like TBoone said, most take 14-18.
How many credits do I need for a major/minor?
Different majors have different requirements, so you'd have to look into that yourself depending on what field you think you're going into.
The links akaCondi pasted should answer all your questions, but hopefully I helped a little.