Yeah, forgot to put this in. For multiclass casting, you prepare and cast your spells from a class as if you were a singleclassed character. Otherwise you'd get abuse like Bard 17/Cleric 1/Druid 1/Wizard 1. Of course, your argument works if you just substitute 3rd level spells in place of the 4th.
Huh. The +6 spells of 1st level never really occurred to me as a problem before, haha.
Actually... a deeper split might be worth it. 6 levels for Extra Attack is probably pretty good, although you might be using the SCAG cantrips, and at that point you might as well go for...
Shame about no multiclassing. Also, I can't seem to fill in the speed or squares boxes, or the ability modifier or saving throw, or the hit dice, or initiative, or 20000 other boxes. Still, this is really, really awesome. Please finish.