Yes, goldfish are very efficient at creating waste. They are also very hardy and can handle a wide range of environmental conditions like pH, temperature, etc.
Both lettuce and strawberries are fairly easy. Lettuce is probably easier. Mint is extremely easy.
It’s not really about the number of plants, but more about the water volume in the system and the amount of growing area. I try to start with one gold fish per gallon of fish tank, and size my grow area based on fish tank size.
There are a bunch of good YouTube videos on the topic. That’s where I learned things when I first started out.
thanks a lot, i have a little pond with mid size koi's looks like an interesting project to redirect the water this summer and feed a few plants to give it a try