Roster Rankup Advice

Just found the forum. So I believe I may have not ranked my team correctly (feels that way). I didn’t have a plan and just played my favorites. Recently I “learned of grinding in the arena” and just ranked most of my 3 stars to 2/20 to compete in the 3* arena. So now I have 36 3* Champs ranked 2/20 with 6 of them at 3/30 (Blade 4/4, Doc Oc, Guilly,W-23, Angela, and Ghostrider). My 4* roster is growing and I want to build towards completing Act 4, the 4* Arena and just a better roster but only have 3 of 18 4* Champs at 3/30(Vodoo,Iceman,Juggs). Any advice on how to rank my roster going forward? THANKS