Sure, you should specify on the AO that the Vayens return to this sheet when defeated. Just to make things a little nastier (and challenging), I'd suggest you that investigators cannot seal a gate if this makes the number of ES on the board equal to the number of Vayens on the AO sheet. Plus, make them roll one die during the final battle. No successes offers you a Blessing. Otherwise the risk is that you have a bunch of blessing investigators slaughtering the poor AO (rolling no successes on two Blessed dice is a 1 in 4 odd)
As for the other stuff... make the monsters have different movement patterns. The Black Light could be flyer. The Burning Wing could be a terrific Stalker (and reduce the awareness of the monster to -2). The Shining Dark as a fast monster, and the White Flame as a static monster (with an awareness of -2).
Your ideas are really interesting, anyway, just spice them up a little!