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synergy? I am clueless on what that is or how to get it.
currently i am farming starship crew: Kylo, Hera's crew, and etc.
The leader abilities and common squad members all compliment each other. So for example here is Hera's leader ability:
The text kind of got cut off but basically having Hera in the leader spot causes all the rest of the Phoenix Squad member to be able to share each others abilities. Hera's leader ability on any other squad is worthless and having Hera as just a member of another squad is kinda worthless cause she isn't that strong of character WITHOUT the rest of Phoenix Squad. Having the whole full squad creates a synergy. Chopper also has some abilities that benefit other Phoenix Squad members. While Ezra and Kanan could also serve as good characters in a Jedi centric squad (with a leader like Bastila who buffs Jedi) they are best served as part of Phoenix Squad.
Now here is Unmasked Kylo Ren leader ability:
Notice how it specifically calls out First Order characters as the ones that benefit from his leader ability. So having other First Order characters (some of which also have specific abilities that have positive effects on First Order characters only) along with Kylo as leader creates a synergy.
A character like Emperor Palpatine has a leader ability that benefits both Sith AND Empire characters so he is versatile and can be used effectively in a few different squad configurations (a Sith squad with Vader, Maul, Dooku etc OR an Empire squad with Vader, Stormtrooper, Tarkin etc).
By looking at the screenshot you posted above you can go down a few paths to put together a strong squad that will give you opportunity to get some higher level characters and have multiple viable squads for all the game modes. You already have Hera (who is not really easy to obtain AND has the Phoenix Squad leader ability) so you're off to a good start if you want to build out the that team. Phoenix is absolutely necessary if you want to get Thrawn (who is one of the best characters in the game) they are also great for Emperor Palpatine because you need either Rebels or Jedi characters to win him.
You can also get an Empire squad going. Vader, Tarkin, maybe Royal Guard. The Magmatrooper is easy to get. You'll have a decent synergy team that won't be super viable as you get higher in level but it could be a good starter team. Eventually if you want a top Empire team you'll need Thrawn, Palpatine etc which means Phoenix is necessary.
Just some suggestions. - really I think it's all about having a team of characters you like. It's only a game after all.
Edit: apologies for spelling and grammar errors. I'm on my mobile.