So, I scored a pump & small pond/waterfall setup on Freecycle: how much trouble have I gotten myself into?

I haven't had the chance to take a look at it yet. I'd guess the "pond" is about 30 gallons, but I'd probably add at least one more tank and do a basic aquaponics setup. I'm not really interested in maximizing output, but rather have a system that 'mostly' maintains itself.

I'm in the foothills of Los Angeles. We have cool weather in winter, including a few light frosts per year, so Tilapia are a little iffy unless I add some kind of protection.