Mekong ray
Yep,and a school of paroon sharks and toss in an arapaima just for the heck of it.
Mekong ray
Since you said tank size and cost are not a problem, id try to get a couple pair of taimen ( endangered trout that can get over 6' found in Mongolia) probably not possible regardless of how much money you have.
A huge tank with several pairs of golden dorado would be cool.
Maybe an Amazon river based tank with a few pairs of each of the largest catfish; rtc tsn jau and Piraiba