The core of a JTR team is JTR, R2-D2, and BB-8. If those three aren't ready to go, and you don't have zetas on JTR's lead and BB-8's Roll with the Punches, you aren't ready to field a JTR team.
Options for the other two slots are many.
The last two slots are very flexible, and options include, but are not limited to, General Kenobi, Old Ben, Amilyn Holdo, L3-37, Kylo Ren Unmasked, Enfys Nest, Thrawn, Han Solo, Commander Luke Skywalker, IG-88, Chopper, Imperial Probe Droid, Resistance Trooper, Scavenger Rey, Wampa, Mother Talzin.