501st questions

Hello everyone, I am farming the 501st. when i get all the members to at least 5* i would like to start using them. My question is who is best for leader? what is the best way to use them? I wont have general skywalker cause i am only lvl 69. I am working on the rest of the members thou. I dont have rex yet. he is like 75/80 shards. right now i have ahsoka, arc trooper and fives. i almost have rex and echo.