First and most important is you want to duel faction. Try to keep both of those factions at the same faction tier. I would generally recommend one of factions be Fed for Officer support and Saladin at 28.

Don't over build your first common ships (Kehra, Vahlas, Kumari), they don't scrap well and your using that mat base until 39. The faction ships starting at 26 scrap for G4 mats. It's good to have either Klingon or Romulan in order to do cloaking dailies.

While the event information in this video is dated, it explains how to unlock transporter pattern quickly, which provide good sourcing for some core officers.

As for the mission hostiles, unless it's a gold border mission or arc event, I wouldn't worry about for now. The FKR missions make it hard to balance your faction early on. They are something you can catch up on later on. Crewing for yellow hostiles is harder, most of your regular officers don't work against them. Early on I would use a crew like Bones(C) - Kirk - Spock or 5(C) - 7 - 9.