Level 68 Looking for Advice

I would get your Phoenix to G8 at least (maybe take Ezra a little farther since you're still using them in arena), but now is usually the time that Phoenix players start to transition into their next arena team. They're probably going to start losing some effectiveness once your opponents start improving their squads (especially the empire ones you've mentioned), but with Thrawn around the corner, you'll want to be ready for that.

As for your farming, definitely keep going with Biggs out of GW until he's finished at 7*. Ditto for Boba. IG-88 is a good toon, but probably not someone you should be making a priority out of the squad arena store. I'd switch to STHan to finish him and then probably Leia since you're already farming Old Ben and Farmboy Luke. At least then you'll be ready for CLS the next time he comes around.

For fleet, getting Biggs will help, and you're definitely right to be grabbing Tie Advanced and Slave 1. I would say those 3 are staples for any good fleet team. I personally would be running Tarkin's capital ship over Ackbar's too. If you do that, make both the imperial and FO tie fighters higher priority. Especially the imperial tie. Keep an eye out for Vader shards in the fleet store too.

So with CLS and ships in mind, maybe push Tarkin up and farm TFP out of the cantina. Your Phoenix will get you Thrawn (you'll want to use your crystals on cantina refreshes to make sure you get Chopper 7*) and Palpatine, so you'll be in good shape for R2 (final piece for CLS). In the meantime, you'll have an alternate team for the arena with Empire.

Work on a Scoundrel team for credit heist's and a Phoenix team for both Thrawn and Emperor Palpatine special events. As long as you have those two teams you're golden. Maybe start working on mod challenges teams like empire, first order, jawa, Jedi, and resistance. Having crit damage mods really help so id say work on a jawa team next. Have a guild already? If not consider joining Galactic Warlordz Reborn.

I would make sure your Phoenix team is ready for Thrawn. Then I would move onto Scoundrels, so you can get the highest tier of the Credit Heist and Training Droid events on farm.