Phoenix Squad Help

Gear 8/9.. around 200 speed on hera, ezra, chopper, health/protection in kannan. Omegad uniques.. under "individual events" there's 430 threads that ask pretty much the same question you are. Read them

The general advice is a minimum of gear tier 8, with most of their omegas, most notably their uniques, and leaving out Sabine more because she's hard to get than for reasons of her usefulness.

Minimums are always bad advice; always aim higher. Ezra in particular is a good one to gear above 8, as he's your principal damage dealer, and the most useful Phoenix outside of Phoenix squad.

The Thrawn event is very difficult. Much more difficult than the Palpatine event.

All that said, even if you don't get seven-star Thrawn next time he comes around, five and six star Thrawn are still arena viable and excellent additions to any Empire or Empire/Sith hybrid team. Or, honestly, any team, because Thrawn loves to pop up in other random factions' teams for that sweet, sweet Fracture.

General recommendations for 7* Thrawn are:
Everyone at 7* (required)
3 or more of the team at gear 9+, other 2 at gear 8+
All shared unique abilities and Hera’s leader ability at level 8 (omega)
Character speed of 180+ for everyone except Kanan
50% potency on Zeb
High protection on Kanan

There are players who have done it with less (typically after dozens or even hundreds of attempts), but those are the general recommendations to be able to get Thrawn at 7* with less than 10 attempts.
If you want to guarantee you get him 7* on the first try, then get everyone to gear 10, get all but Kanan to 200+ speed, and omega everything, in addition to the other suggestions. If you want the battle to be trivially easy, push to gear 11, 220 speed, and zetas.