research any Monster impulse buys. chances are they will still be there when you go back as they hardly fly off the shelves.
Monster fish = lots of work. the right food and lots of it, exceptional water quality, correct tankmates etc.
I reiterate my previous point, a huge tank with lots of small fish in it (think several species) is infinitely more impressive and interesting than a single huge fish.
I had the room for stingrays, FRT and other monsters but I can't really justify spending that kind of money on a fish that I don't really have any interest in keeping that is difficult to keep.
At the end of the day people online will only give you suggestions and ultimately you should stock what you want or you will just end up trading them in for something else.
good luck with your set up!
Here are a few pictures of my old monsters
x12 full sized red tail tinfoils. They used every gallon of my 225
x2 albino Pacú, I had these guys for a while until they outgrew and went to a pond
Giant snakehead, grew from 2,5"-6" in about 2 weeks
GG, very aggressive towards anything shiny, especially tinfoils. Its the reason why I had so many.
My florida gar spent 50% of his time lounging, 50% stalking prey
I didn't keep all these fish in the tank at the same time obviously things changed up over the years but ultimately before I had to sell the tank (it wouldnt fit in my new house) I switched back to small peaceful fish, less of a headache and it was very intersting to see how they interact with eachother in such a large environment.