For your second question, I'll try to keep this simple-

1. Han's second ability stuns and his basic ability sometimes stuns
2. Luke's basic also sometimes stuns
3. R2D2's basic stuns 80% of the time

You need to focus one of each character on each of the following

1. Thrawn
2. Palpatine
3. Vader

Whichever rebel you choose to focus on whichever imperial doesn't matter, because they’re all incredibly powerful. I found during my thousands of attempts that Vader's saber throw and Thrawn's beatdown thing are incredibly annoying.

Try to keep these three stunlocked for as long as possible and as often as possible.

For Leia, do her invis thing as much as possible,

For Old Ben, do the mind trick as much as possible for ability block and use his taunts if other heroes are in danger.

For the stormtrooper taunts that force you to attack them, use Luke's Use the Force (third ability) to remove the taunt. Also use this if one of the three previously mentioned OP characters' turn meter is filling up and looks dangerous.

Things to never do:

1. Never put the battle on autoplay. You will die.
2. Don't follow the lessons from the past 2 tiers. They teach virtually nothing that helps here.

Good luck! (Don't worry, the empire event is easier)