For Separatist Might I'd recommend getting the Chimaera, keep building your HT and start building your separatist ships for the fleet missions. Geonosian ships are also great if you wish to stay on top ranks in fleet arena. Geonosians (all 5) and separatist droids are great in Separatist Might and are required for some of the missions. Once you unlock Traya the Sith triumvirate is great too (Traya, Nihilus and Sion). Night sisters do well too and until you begin seeing solos in hSTR they are great there as well for phase 3 and 4 (Talzin lead zeta, Asajj, Daka, zombie + 1 for TB. Replace zombie for paper initiate and add JKA for hSTR).
If you're going for a GL I'd recommend going for SLKR first since he's required if you wish to solo hSTR and also great in TB (and squad arena).
I wouldn't recommend building teams for LS Hoth TB specifically since at some point you will move on from there to Republic Offensive (LS Geonosis TB). Padmé, JKR and 501st teams (GAS/Shaak Ti lead) are great in Republic Offensive.
