For your first pair of shorts, I'd definitely recommend going the the LBS. You don't have to ask them anything; just try on the shorts.
Shorts shouldn't be baggy; part of the reason they're tight is to act as "compression shorts," which helps your leg muscles work more efficiently. But they shouldn't be so tight that they're uncomfortable.
The pad *will* feel like it's bulging out all over the first few times you wear biking shorts. After a while, you get used to it and just don't notice it anymore.