I have been a member of USRSA for several years and I find their resources quite valuable, especially their archive of patterns for obsolete frames. I have not, however, determined a need for the extra expense of CRT/MRT certification, although it's a good idea to study and practice as if you had to take the test.
Keep your inventory simple at first. PSGD or Wilson Extreme are well known. Maybe a set or two of Red Alert for stringbreakers who are not ready for poly.
The mini reels of Sensation are a good buy right now. It is also well known although at reg price, I'd opt for Prince Premier Attack.
The well known polys (Big Banger and RPM) are not good values for you or your clients.
The Big Hitter strings are a good option here, as most players are aware of the Tourna brand, if not their strings
Neos 1000, Eagnas Combo 810