OK let's re-examine this concept and snazz it up a bit. It is novel enough but we've got to apply some critical thought to it to make it worthwhile.
First off, it's got to be thin & crispy & hollow crust, otherwise it's going to be a hassle to eat. Bam, easy one.
Next up, toppings: do we want each tier to have the same toppings or mix it up more in the same level? Bottom level's got to be mostly thin-shaved meats, I think, so we'll throw on some peperoni or whatever you've got plus crumbled ground beef/sausage, but not too much. Second layer would be chicken/spinach/roasted red peppers by my preference, and then I think I'd want the top guys to be cheesey mostly, so lets hit them with mozza, feta, parmesean, and, I don't know, a little bit of blue? Would probably put mozza parmesean on all of the mini-pizzas, and then half of them get feta and half of them get blue cheese, yes, that will work. That would be my first thought.
I know some people like barbecue chicken pizza, but frankly, I can not get behind that shit. If you were so inclined, making the middle layer a barbecue chicken layer could certainly be nice, but apart from that I am trying to think of more sauce variations to use here. Could always cook a bunch of dried tomatoes in with the sauce for the top or maybe middle layers to punch up the acidity like mad for a contrasting level of flavour. Some garlic-cheesey white sauce marbled in with the tomato sauce on one of the layers could be interesting too?