The only limiting I do is timing when I claim my dailies. If I have full energy and I level up then I'm in excess and I won't regenerate any more, so I check in the top left corner of my daily rewards screen and it tells you how far away you are from leveling up. Then I make sure I don't pass that point until I have only a little energy left so as not to waste it. Other than that, all out. Out of my top 10 heroes I only have one that I can obtain gear for, so I need to level up pronto.