KRU and his ship are on the same cantina node. start there.
Vader and his ship are really important. so is TFP and his ship. Vader's ship comes from 1 slot in the fleet arena store. His shards are lower in the store or achievements. (also a hard node, but you're not there yet) TFP ship shards can come from galactic war store.
Biggs is good for raids as part of a wiggs or rebels team and arguably the best ship in the game.
Phoenix ships are ok if you've already farmed them for Thrawn/Emperor.
And when it starts to hurt, remember that the ship ability material challenge can award Zetas, and is critical for character development.