I have a 48 x 24 x 24 ; 120 gal tank... it's a nice looking tank and I'm sure your's with the extra height is even nicer...
The 24" front to back is appreciated by every fish in the tank... but the 48" length limits the quantity of fish it can comfortably hold...
So to me a tank such as this would be more suited for a smaller number of Larger fish... I have Trimacs growing out in mine and in the long run the tank will house a pair of Trimacs and a pair of Cons for as long as the Trimacs permit.
One thing to remember though, is although your tank has "limited floor space" you can do some extensive aquascaping and create cave structures which in essence increases floor space by creating a shelf like approach. I'll attach a picture of a tank I used this approach with.
One big concern with such complex structures is ensuring you have proper current throughout the tank. No fish will want to occupy a stagnant cave no matter how well it is situated. Collecting/controlling waste is also more difficult with such rock work.
…If you are dead set on the Dempsey pair then I’d suggest them with an Oscar and a pair of Cons as long as the others permit… Obviously you’ll want to start off with an Oscar with some size on him so he will be able to cope with your Dempsey pair… although I would start with a small pair of Cons…
The tank has enough volume to support this stock list but it will be your job to create the caves/structures to allow each to have enough turf. Insufficient aquascaping will make things very difficult for the Oscar and probably Cons…
