It is easier to get one or two Phoenix units to G10 or 11 than it is to get all of them to G9 because of how many stun guns the faction takes.
The Palpatine event is almost trivial now. The gear cap and level cap were lower when that event was released, and mods did not exist. You'll be fine as you are for Palpatine.
G8 with good mods is generally regarded as the floor for seven star Thrawn, but I suggest going higher on at least one unit. Ezra is the most flexible unit later on, so he's a popular choice as the one unit to take beyond G8 early on, and his damage output is the backbone of taking enemies down in the Thrawn event.
