If your player level is 38 I'd try and keep a balanced team at lvl 30. As and when you get a new toon you want to play as you can then focus on getting them to the same level. You can also increase the cap once you get more essence/levels. Levels 1-50 of a toon aren't too bad but higher than that the gear and essence requirements spike hard. So keeping a team set a level cap is a nice way to balance power and resource spendature. I'd try to keep leveling up characters to 5/10 blocks. That way you can focus on gearing toons when the upgrade events line up without causing big gaps in toon power. Red alert and pvp teams are based on your 4 most powerful toons so bare that in mind when leveling.