TL;DR: Speed is king. They'll have enough potency from a potency cross, Palp's leadership, and the two potency mods. DV: speed, potency; Thrawn: S, CC (or whatever); EP: S, P; GMT: S, P; TFP: CD, CC.
Check out: https://swgoh.gg/stats/mod-meta-report/guilds_100_gp/
Long Version:
Those mod advice pages are both good starting points, though I've occasionally disagreed with their reasoning, and I'm not sure how often they're updated.
I think the most useful tool is this: https://swgoh.gg/stats/mod-meta-report/guilds_100_gp/
It basically gives you the rundown of how the biggest, most successful players mod their characters. If you click on a character name, you'll see a breakdown by percentage of how players have modded them—not only which set types, but which primary attributes are most often used in each slot. It's a great way to see the general consensus/practice of serious players as well as what the range of viable alternatives might be.
The general rule of thumb for arena is that speed wins. For your team especially, you need to get the jump out of the gate.
If you have Palpatine's leadership zeta, dump all possible speed into Vader—that plus his unique should get him enough speed to go first, use crush, dispel with saber throw, and that should give enough TM to get the rest of the team started. Thrawn should go next, giving his turn to EP. The objective is to get to EP's mass stun ASAP, and fast Vader and Thrawn are the tools to do it. (Vader's base speed isn't amazing, so if you can get better total speed using other mods with speed secondaries, go for it. But secondaries being equal, the speed set is obviously ideal.)
If you don't have Palp's leadership zeta, then go all out speed into Thrawn so he can give a turn to EP.
A fast Tarkin can remove TM from the other team before they get going (but watch out for counters). TFP has good base speed already so should be more focused on damage; a lot of his TM will come from his unique
Hope this helps. Good luck!
