Stock tank in yard for fish

I was thinking about putting a 200 or maybe 300 gallon stock tank on my back yard. I can provide aeration. I thought I might run the gutter downspout into it so parts of the year a lot of water would be replaced and the rest of the time, I could use buckets.  Water is pretty expensive here and I'm semiretired. Another option is the water from the sump pump in my basement. Even when it's dry my dehumidifier puts a couple gallons a day into it. I know I'd need to use some city water.

I guess I'm wondering if this would work and if I could produce some fish to eat this way?  How many fish could I put in it? It would probably be channel catfish. Maybe tilapia. If it would not produce many fish, maybe I could catch fish and use it as a holding tank and maybe grow some smaller fish to a bigger size?

I'm going to try this as a modified aquaponics system.  I have three smaller stock tanks, one of which will have fish, and the other two will have water plants for filtration.  I'll also have a flood/drain gravel bed for more filtration and to grow some plants which prefer not to be immersed constantly.  I'll be using a circulating pump at least part of the time.  I almost had success with a similar system a few years ago but I bought new fish who brought a disease into the system and all my fish died.  The fish who were doing well were Hybrid Bluegills; the fish who got sick and killed everyone were Channel Catfish.  No more catfish for me!  They were creepy anyway.  I hope to get new Bluegills next year.  They have the advantage of being incredibly tough, not picky about size of tank or temperatures, and will grow to pan size in a small space (even a fish tank).  I will be raising live feed for mine - Red Wigglers and Black Soldier Fly larvae.

So I think you might want to set up some kind of filtration system for your tank, which would enable you to not need to change the water, but just replace what is lost to evaporation. For aquaponics inspiration I like Murray Hallam's videos  http://www.aquaponics.net.au/   but there are many other sites out there which may be helpful.