Once you’re not relying on your 2-stars to win matches, yes. Keep the ones you lean on max-champed and farm the ones you don’t use. It may even behoove you to start duplicates of the 2-stars you use.
Tokens. Chase those Elite and Heroic tokens. 2-star champ level rewards. DDQ. PvE progression rewards. If you get an elite 3-star (IM40, Strange, Thanos, Fist, Switch, Kamala, Mags, etc) to 11-12 covers don’t be afraid to spend the 20 CP to finish them off and get them champed. As for 4-star covers, they’ll start to trickle in while you’re building your threes. Once you have a few 3-stars champed consider making the jump to SCL 7 in PvE where you can get a 4-star progression reward.