As for a scope for the Max, I would go with a low, fixed power scope in either 1x, 2x, or at most 3x. Especially if you're shooting primarily off hand at 25 yards. The fixed power scopes will be less expensive (all things being equal quality-wise). Look on the classifieds here, there are deals that come up all the time on TC, Nikon, Leupold brand scopes that will be very good scopes for your purpose.
As far as your grip goes, this gets into more of a personal preference thing. I personally don't care for the pachmyer grip shape. But that's just me, some guys really like them. That's fine. Try one and see how you like it. They are also easy to sell if you find you don't prefer it. Nice thing about Contender stuff, it's easy to move when it's time to go.
For your grip technique, I would change your off hand to either wrap your fingers around the front of the trigger guard, or hold the rear of the fore end. On my boomers, I wrap my index and middle fingers around the front of the trigger guard. On my smaller caliber stuff, I usually shoot it one handed. Also, try it from the bench, off of a front rest. Or, even better, from a good front rest (rifle rest type), and a rear flat bag to put the butt of the grip on. You will be amazed at the accuracy of the Contender platform when shot this way. It will easily rival a bolt action rifle.
Like this:
As far as where to get more barrels...
LOL, from everywhere of course!
I've got some great deals both off of this forum's classifieds, as well as the Specialty Pistols classifieds. You have to shop around, and be prepared to jump when you see one you want. They usually go pretty fast. I think I would go with something different than just a longer Max bbl. Maybe a 223, or a 30-30, or a 22 hornet, or if you like boomers, a 45-70, or a 375 JDJ
. I prefer the 14" barrels for pistols myself, but that again, is just personal preference.
Also contact Ed's TC's, a sponsor here, he has A LOT of TC barrels.
Enjoy.