To your last question, my GS is 5 stars and I don't use him in arena, only in GW. I also don't use him as a pilot anymore since I have Slave and Scimitar. But he will be needed as 5th dark side pilot and when ackbar has 5 stars, as reinforcement.
However Wedge I need in Arena, so get him first.
The long farm ships (Slave, scimitar) are actually not that slow. I have Slave ready and soon scimitar 4*, but with lvl 77 the pilots seem to be too low level. @Doitsuyama posted his setup, he used pilots with more than lvl 80.
So yes, the dark side ships can be SF, GS, TFP, Slave, Scimitar.
My light side ships will be Wedge Biggs Ahsoka JC and either Rex and/or Clone Sgt + my lvl1 Bistans.
I currently farm both Rex's ship in fleet store and CS ARC in GW. Both slow farms but I will need like 10-15 mio credits for my pilots (some are still lvl 60) and lvl 80, and this will take some time, too...