1) I feel bands work better than DBs, but cables are even superior (they provide exactly the same tension throughout all the movement);
2) I used to think the same, but since I started subscapularis work (internal rotation), my right shoulder feels more stable while benchpressing;
3) I wish I had started training with the same mindset
I split prehab exercises in three: rotator cuff work, scapular work and rear delt work.
You already work your rotator cuff, that's good! For scapular work you can do wall slides, face pulls, prone lateral raises along with serratus activation (push up plus, swiss ball push ups...); for rear delts, bent over flies should be enough to keep shoulders balanced.