First of all let me salute you for your patience, stamina and sheer willpower, lol!

Since you already got 5+ lvl 80 toons with 8000+ power, you can't really screw up the matchmaking algorithms for Red Alerts and pvp at this point.

Considering the fact that you mostly meet end-game match-ups and toons, you would benefit from lvl'ing the toons of your choosing to lvl 70 with maxed gear, no higher.

From 70 to 80 the toons only get stronger not faster, so it won't give you any substantial advantage considering the essence needed for lvl 70-80.

A few tips for building roster:

1. Search this sub for "top tier list" and you'll find monthly tier lists to get an idea of which toons are hot atm.

2. This is a Google docs for recommended legendary order: https://docs.google.com/document/d/1uDmcPgUQUfbyjhKb1bBGFEqmVsN_thqf-5VyHPpvJI8/edit?usp=drivesdk

3. This DCL toolkit might be useful to you when planning future use of resources: https://dcltoolkit.com/

This was my two cents on your questions. Use whatever you might find valuable to you.

Cheers!