That's alot of cichlids, what type of Severums? I'm not gonna lie at first I pictured a giant 7ft tall collum tank. But I'm going to assuming your tank is 84Lx30Wx31T. I imagine it's gonna be an absolute stunner just with cichlids.
Now it could work, with the cichlids you have listed up there. We could think the acara's mind their own while the Severums are too busy chasing each other to hunt the acara's.
But, at the end you mentioned blue acara's. So are you going to mix Electric blue acara's with regular blue's? There could be some issue there, seeing how electric blue's can be kinda soft and tend to stress easy.
Also what type of Geo? I know everyone views them as small but here is a 11 inch one.
Also I have a Green Severum that is pushing 10inches.
And here is a chocolate that is around 8-9
(Sorry for the poor phone pics)
Anyways my point is, when you start talking about 18, 9inch fish, 10,10,inch fish ect ect. Even that mighty 7ft tank starts to look cramped.
Can it work? I think so, absolutely. Will you be over stocked. Yes in the long run. But, as time goes by you may decide to switch things up and change things around. My Severum up there is about 12 years old ish. Give or take a year or so. And that Geo is at least 7, because the guy that has his has had him for 6.
Your gonna get some pairing, some minor squabbles here and there. But all and all I think if you start small it's not gonna go south too fast.
But, that's just my 2¢