Here's my take on this:
- RGT can reach 36" long, probably won't get over 24" long though
- Snakeheads can reach about 24" long, maybe a bit bigger
- PBass can reach about 30" long, maybe a bit bigger
- Bichirs can reach 30" long, probably won't get over 24" long though
- Motoro Ray can reach 36" wide, probably will top out at a little over 24" wide though
- Koi depend on the strain - most top out at around 15" long but some strains can reach 36"
Now, the only fish out of your list that I have personally kept would be the koi - however I've researched keeping monster fish extensively, and my personal views on tank sizes would be:
- A single adult RGT deserves a tank with an 8x3 footprint
- A pair of adult emperor snakeheads deserves a tank with an 8x3 footprint, as well
- A pair of adult mono pbass deserves a tank with at least an 8x4 footprint and preferably larger
- A pair of adult endlicheri bichirs deserves a 5x2 footprint at least
- A single adult motoro ray deserves a footprint of 10x4
- A trio of adult koi deserves AT LEAST a tank with an 8x3 footprint, but would be better suited in a 500+ gallon pond
A lot of people will see my views on fish-keeping as a bit odd, but I would prefer to give the fish as much space as I could - and if I didn't feel that I could give the fish sufficient space, I wouldn't keep it. That being said, your tank is overstocked by quite a bit. Drstrangelove's calculator is an awesome tool, hopefully he doesn't mind me saving it to use at some point.
In your 5x2x2, the two endlicheris would be able to stay, but that's about it, in the long run. If you wanted to keep all of the fish - my personal opinion would be to move everything into a tank with a 10x4 footprint, save for the koi - either build them a pond or relocate them to somebody who does. For three "normal" koi, a 500 gallon unfiltered pond would likely be fine.
Just my personal opinion - take it with a grain of salt as I haven't actually kept most of the fish you're talking about. But these are my beliefs on keeping monster fish.