If I use "brutality" or "rapid fire" or "pummel" etc. can I use "opportunistic" after the first attack (Use after a hostile figure suffers dmg. You gain 3 movement points) to move before my next attack? My assumption is no since it says "gain 3 movement points" which would go in your bank instead of "move 3 spaces" which would happen immediately and interrupt.

Another question about opportunistic, lets say my Greedo attacks and deals damage, can I play opportunistic to move a different figure than the one who is activate?

You can play opportunistic on any mercenary figure after a hostile figure takes damage.

If you play it on the figure whose activation it is, then they just gain the movement but have no opportunity to spend it if you're in the middle of something else.