I think my fleet was around 280k go when I 3 starred it. Chimera lead. HT, silencer and imperial tie starting. Tie advanced, ghost and slave1 reserves. Only bring in slave 1 if I needed cannon fodder
I'd recommend investing in Hound's tooth. It's still the best ship out there, and will make a lot of things easier, ship-wise. You could probably 3* it with your current fleet and a hounds tooth. Run Silencer, HT, ITF. For reinforcements I'd go with TIE Advanced, Scimitar, and then either Ahsoka or Slave 1. Also, unlike squad battles, you can get 3* with one defeated ship.
One more thing that may help is unlocking Chimaera. It's a generally better ship than Executrix, especially for campaign, since it can heal/control TM.
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Pair Hound’s Tooth with your silencer and Vader, and that’s how I 3 starred it. If that’s the Enfys Node, just know that that is a really long farm.
So what fleet is your enemy at 5A (Hard)? If rebels, then empire with TIE Bomber probably minimizes gear investment.
So on & so forth. It's often just as much about who you use as it is about how far they're upgraded.
One more thing that may help is unlocking Chimaera. It's a generally better ship than Executrix, especially for campaign, since it can heal/control TM.