A blue Aizen team looks fun, but you probably want to prioritize monsters with a dark main attribute, aside from monsters like Blonia (great stat stick, nice active, good enough awakenings). And you definitely want to prioritize monsters that make dark orbs.
The only thing Aizen does with the water attribute is give water monsters 2x RCV. Water orb matches will activate
nothing extra in his leader skill, and there is no attack multiplier bonus for monsters with a water attribute. In comparison, matching 5 dark orbs in a cross shape will activate the additional attack multiplier in his leader skill to make your attack multiplier go from 36x to 144x (or even higher if you make more than one dark cross).
So...
This is your PADHerder, right? Kick Alrescha in favor of Castor (I'M JEALOUS, BTW). Or if you want to wait until you've developed Castor, then put in Revo Voice. Or maybe Satsuki. Or Gryps Rider. Basically any dark monster other than Alrescha, because her active barely does anything for an Aizen team compared to other dark orb changers (see what I said earlier about what you can activate with water orbs vs dark orbs).
Aizen teams aren't tank teams, so you want to prioritize whatever will make your damage go up (e.g. the attack multiplier). Treat that "2x RCV for water monsters" as a bonus rather than something of high priority--unless you're reeaally lacking in RCV, in which case you can give it a higher priority. (Similarly, don't prioritize HP very strongly unless you're reeaally lacking in HP and/or you want to use Aizen to get through a dungeon with at least one heavy preemptive, etc)
Why do I keep typing walls of text TT_____TT
Disclaimer: I don't actually play Aizen; all of the above is made up of my best guesses, since teambuilding based on leader skills is basically the same lol I didn't include much about which actives you should bring, aside from "if you have a dark orb changer and a water orb changer, put in the dark orb changer instead of the water orb changer"--which is basically a corollary of teambuilding based on leader skills