1) Vader is ok under EP lead and his own leadership (when zeta'd), but not the best empire toon out there and not suitable for thrawn lead. Tarkin is fine, even great, for offense (since you can charge his special for extra damage), but on defense he's going to drop like a rock. It depends on your level and who you can get, but the most commonly used hign-ranked empire team is Thrawn (l) DT Shore Storm and Veers/EP/Krennic. I personally run EP (l) Thrawn DT Shore Krennic, and loving it.