Stack all your best units for your helper squad then switch from team 1 to team 2 as your main squad if you want more balanced teams like you have. Better helper squad the more appealing you look to friends and be able to keep strong friends lets you punch above your own weight.
Check which units have a desirable evolved skill and go for evolving them first and foremost to increase your effective power through passive skills.
Use Affection items on your units you intend to evolve sooner rather than later, affection bonuses double when evolved and evolving reduces a unit's power so high affection can minimize power loss or result in a gain in some stats.
Get rid of the 2* units as soon as possible 2* units don't get a skill when evolved so any exp you're giving the is wasted completely, your 3* units should eventually be replaced, but an evolved 3* still has a skill if you find yourself with not 4*+ to evolve and a 3* with a type advantage can still be more useful than a 4*.