I would say to work on your darkside ships and pilots. When you get the last star on Hera, start farming TFP followed by KRU (getting the toon and his ship from the same shard is huge) in the cantina. Stop farming whoever you're currently farming in the GW store and get Biggs to 7* ASAP. While not DS, he's arguably the most important ship in the game and a quick farm (he's a good rebel toon as well). In fact, after you have Biggs to 7*, I would farm the remaining toons in that store only one shard purchase a day. Use the rest on ship shards (Biggs and TFP show up there regularly). When you finish Chopper, get Boba Fett to 7*. Keep 400 Fleet currency handy for when Vader/Boba's ship shows up. They're a longer farm because they aren't always showing, but definitely worth it.
I wouldn't focus on Phoenix ships just yet. Use that fleet currency on others first. Phoenix ships are good, but you can have a fleet without them and you need the DS ships to get zeta materials.
By the time Palpatine comes around again, you'll be able to get him at 7* and your interim arena team will be set (EP, Thrawn, Vader, Tarkin, and TFP) until you can get Sion up a bit (he works at 3/4*, but I don't know about 2*).
Now that mods have their own currency and you don't need different factions to get each set, I would take your Phoenix team and unlock all the Tier 3 challenges. If you haven't gone through all the battles yet, just unlock what challenges you can and start farming T3 on whichever set you like until you've got yourself at least one team's worth of quality mods. Then you can move on to unlocking all the others.
As far as ships go, Biggs/Vader/TIE is a pretty insane setup - out of the top 20 teams in my fleet shard, me and like one other guy are using something else. And Biggs & TIE are pretty easy to get, though Vader's ship is a long farm to 7*.
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I would focus on getting a 7 star EP the next time event rolls around, and then use EP, Thrawn, Sion, Vader and Tarkin.
As for arena team now, Bastilla maybe? I m not sure
I wouldn't focus on Phoenix ships just yet. Use that fleet currency on others first. Phoenix ships are good, but you can have a fleet without them and you need the DS ships to get zeta materials.
By the time Palpatine comes around again, you'll be able to get him at 7* and your interim arena team will be set (EP, Thrawn, Vader, Tarkin, and TFP) until you can get Sion up a bit (he works at 3/4*, but I don't know about 2*).
Now that mods have their own currency and you don't need different factions to get each set, I would take your Phoenix team and unlock all the Tier 3 challenges. If you haven't gone through all the battles yet, just unlock what challenges you can and start farming T3 on whichever set you like until you've got yourself at least one team's worth of quality mods. Then you can move on to unlocking all the others.