Do I go for JTR or do I round out other squads first?

Well considering JTR will be here in the next few weeks, you'd be looking ahead a ways. You're not even in a place to get 5* BB8, leaving you 7 toons you need to 7* for JTR, 4 of whom you can't even farm yet.

If JTR is your goal, then start working on FO to be ready to grab 7* BB8, then look to Finn/Res Trooper/Vets.

Otherwise, work on what you want most. JTR comes back every so often, so it's not like if you miss her now you'll never see her again.