In my backyard is a wooden deck surrounding what used to be a large, above-ground swimming pool. I want to reuse the structure without installing and filling up a new pool (way too wasteful in this Texas drought!). I'm looking for advice on making a fish pond out of it... Tilapia most likely would be what I use, since they're popular and probably easy to obtain, though I haven't looked into fish just yet. Ideally I'd be able to build an aquaponics garden out of it, since I think even if it were half-full the pool area would be too large for a manageable fish pond. However, it may be better just to get the fish going first and ease into creating a new garden.
Anyway, the pool vinyl is badly damaged and will need to come out. I'm not really sure what would be an efficient method of walling in the pond, as the edges of the pool are nearly 4 feet deep and I think that would be a whole lot of dirt to bring in. I think I need some way to turn half the pool into a fish pond and keep the other for possible gardening, but I've never done anything like this before. I don't even really know where to start!
Either way if your going artificial then you need a new liner and I would suggest a pond liner if not two. Your main issue is going to be keeping the water clean if you get any sort of density building up. I know of several people who have koi ponds as big as you describe with an aquaponics component to them and they still have to run bio filters and spiral filters to keep it clean!
My suggestion given your experience is to start small. Your in Texas so finding a couple IBC's shouldn't be hard. Start there if your not ready to put in a permanent pond (or cant) and get a feel for it. By the time you get things figured out you will have a better idea of what to do and you will have a stock of fish to pull from to do it.
I say this because there are a ton of IBC systems established already and they are nearly plug and play at this point.