I've been working on an empire team as well...
Tarkin (L), RG, Vader and magma... I just swapped out my snowtrooper for the Tusken shaman and he has a really nice synergy and gives an empire team a solid healer option.
Even with my Vader and magma at only 5 stars this group can still compete in the top 10 on my server and does surprisingly well when I run them instead of the standard Dooku or QGJ lead team.
I think I may focus on this group initially with the upcoming level increase and combat changes and see how they fare.