Lol, you're not quite ready for 6.4 yet. You can surely do it, but I advise you rank up a bunch of Champs to rank 5/rank 2 to relieve you of a lot of stress.
That being said, I'd take up G99, Quake, AA, aegon and maybe Colossus as 5*s. As for 6*s, you've got an insane set! You don't really need any more 6*s ranked up for now in order to save your tier 5 basics. Also, mags can handle darkhawk (which is the major fight you'd probably use him for) at rank 1 quite well.
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That being said, I'd take up G99, Quake, AA, aegon and maybe Colossus as 5*s. As for 6*s, you've got an insane set! You don't really need any more 6*s ranked up for now in order to save your tier 5 basics. Also, mags can handle darkhawk (which is the major fight you'd probably use him for) at rank 1 quite well.