You're correct in your assumption that bang can only jump cancel 2b on block. Other than that he can jump cancel any Drive attacks on block, however - they shouldn't be used in blockstrings because they're incredibly slow. So if you're fighting a nail pressure bang, 2b will most likely always lead to tk nails.
Bang shouldn't be throwing 3c out in this fight, it's really unsafe and not worth the trouble when you can zone ragna pretty well anyway.
And yeah, if you block bangs drive moves (Any of them.) Bang needs to jump cancel, if he doesn't and stays on the ground, it can end his pressure in alot of cases.