Also, a good dark side team could be Palp, Vader, Thrawn, Sion and Nihilus but you might need to gear/star up Nihilus and Sion a little. You could also sub in Bastila Shan fallen into the sith with thrawn lineup. Or you could have Nihilus lead the Sith and you put in Count Dooku which supercharges Dooku because he will have a high health steal plus he counter attacks a lot so whenever he is attacked he will counter attack and just keep getting more health.
I also don't think I see Palp but you could unlock him with rebels and should be able to gear him up to hopefully at least purple.
Another Palp lineup if you don't want sith with thrawn is full empire lineup with Palp, Vader, Thrawn, Tarkin and Stormtrooper.
All in all, you have a lot of options and variations for lineups but you should just go with what you what. Although I recommend to go with Sith or Empire, you get the final decision.