Supercat 17 is a great boat. If all the bits and trailer are in good shape sounds like a good deal.

I'm guessing the license you are refering to is the one that some states are requiring now if you were born after a certain date. Usually to get those you need to go to some safe boating courses (USCG Auxilliary), but I don't think you need full-on sailing classes to get those. Being the military you might want to check to see if there is a sailing club associated with the base - that can be one of the better deals for getting lessons. As an example, where I work (Goddard Space Flight Center) there is a sailing club that has a fleet of Flying Scots. To join, get lessons, and be club certified to check out club boats is around $150. You might research things like that where you're stationed now or where you're heading.