general recommendation is:
Level up 3-Star Champion to Level 12 (3 Runs, or use 1 XP Brew to Level 10)
Level up 4-Star Champion to Level 19 (7 Runs, or use 3 XP Brew to Level 18)
personally I only do 5 runs on 4 star to get them to lvl 16. the rest I do as written above