Not sure what lvl of gear I had at lvl 36, what I can say is that gear is as important as stars or lvls. Get as much as you can as fast as you can, and you can't go wrong!
I'd say gear is probably more important than anything else. You should be constantly meeting the boundary of either a level cap or mission unlock so you have the maximum at all times. I didn't farm hard enough so the competition started to get harder, then I went all out and now I have 9 heroes at 6*. Eventually you meet the barrier again and then it's time to farm shards.
Note: Only gear heroes you plan on keeping. Don't waste your resources.
In my opinion order of importance
Gear
Level
Ability level
Star
My name is cosmicturtle333, aka CT-333, aka Threes.
I started to get and upgrade toons for challenges. I gear them up with the gear that's not usable by my higher lvl main characters. Lvl 40 is easy enough to train to, and a lvl 40 gear 5 toon is good for all the challenges (teamed with the couple of high lvl toons that qualify for them). Completing top tier challenges is mandatory to gear your mains. Which I agree with the last poster, should be priority number 1. Levels and stars will come in almost no matter what else you do.
Replies
Note: Only gear heroes you plan on keeping. Don't waste your resources.
In my opinion order of importance
Gear
Level
Ability level
Star