Blind goldfish need no special care. Just don't rearrange the tank decorations, they memorize them. There even use to be a blind lineage of goldfish. It's probably extinct now. I've not seen any for sale in my lifetime.
Well, if I had that bioload - say in a broken-tank emergency - I'd be doing at least 50% water changes once a day, and I would not be feeding the animals AT ALL. The one big white goldfish alone is looking at (with a once-weekly water change and light feeding, the general goal of most hobbyists) a 55 to 75 gallon tank minimum, bigger the better. With emergent plants. And a slew of filtration.
The turtle is a whole other galaxy. Being young, it should be eating at least twice a day. That could, under the right circumstances, produce more ammonia than the goldfish combined. You're looking at a 120g, IMO, at the least.
But I should add to your peace of mind that goldfish and turtles are both hardy! Do lots of water changes and only feed the bare minimum, and you can bide your time.
Do obtain some filter muck from a healthy tank and dump as much in there as you can. There should never be any ammonia! You might be killing your bacteria, because you should have nitrates in the hundreds, and you don't.
Gouramies used to be very hardy, but are now weaker thanks to inbreeding. He might do fine, he might not. Just do your best!