Welcome John, sounds like you have a wealth of gaming experience and familiarity with fantasy maps to bring to bear on map creation. As you mentioned, there are several great tutorials here to help you get started. Once you find one you like and have begun to play around with it, post up your work, be it ever so humble, in a WIP forum and ask for constructive criticism. You can learn quite a bit about map-making that way. Best wishes in your new endeavor.

Cheers,
-Arsheesh