What does Plekostom eat

Do tankmates tolerate giant gourami?

I wouldn't recommend keeping the giant gourami with any of the fish you have in tank 2. Many of your other fish will likely be eaten by the gourami. In addition, some of the fish currently housed together in Tank 2 are incompatible in the long term.

Koi should not be kept in tropical temperatures. If they are kept warm enough in temperatures so that all the other fish in that tank can speed up their metabolism, strain their systems and drastically reduce their life expectancy.

Your silver sharks will likely grow large enough to be a threat to many of the other fish in this tank.

Your Pleco may at some point try to eat the slime from other fish in the tank. This makes them prone to infection and disease.

The giant gourami can potentially be longer than two feet and will require a huge tank even if kept on its own. All other fish in the tank would have to be large enough not to be eaten and either robust / armored enough or agile enough not to be injured by the gourami. Adding larger fish can mean increasing the required tank dimensions even further! For a large fully grown specimen, you're already seeing a tank measuring approximately 6 'x 2' x 2 '(or ~ 180 US gallons)! You can potentially get away with a more modest tank (100 or 125 gallons), if Their particular gourami only grows up to 18 inches, which seems more typical of captive specimens, but there is no guarantee that it will.

The Pleco (if it's an "ordinary" Pleco) also has the potential to reach 18 to 24 inches in length. Just like the koi. The sharks will likely be in the 12 to 14 inches range when fully grown.

It is best to have three or four separate tanks for all of the fish you list. If this is not practical for you at this point, it may be best to bring some of the fish home. There might be another fish lover in your area who would be excited to adopt some of you, or there might be a pet store ready to take them over.