First of all, well done for saving up that much money and for putting it towards this hobby! Second of all, while you are okay with spending that much money on a fish tank which is 200 gallons, I feel that you would be able to get one that size (and even much bigger!) for a much cheaper price. And while I do agree with Jantaris in saying that it is none of our business about how you want to spend your money, i'd hate to see you spend that much money on a tank and then see a bigger one at a better price in a few months time. Presuming you've researched tank prices and this is the best you've found, however - then I say go for it!
As for your stock, I do agree with everyone here about how hard it is to keep stingrays. You may not know this, but when they are ill (which is very common) you have to inject medicine into them due to their lack of fins. If you do want to try this out though and see how it is to keep stingrays, then I say you should consider it! If you do want a stingray though then I suggest you try and find a teacup stingray (make sure it's the real one though). As for your final stocking list, however, I say you take out thee red-bellied pacu indefinitely and then the arowana. You could add a sturgeon instead if you like those? I'm probably going to get killed for suggesting a sturgeon lol.
Good Luck!