Bowl,5Gal,10Gal,30Gal........

try craigslist.org and any free or cheap classified resources in your area. buying used can save you a lot of money, and might let you go bigger. no need for a ugf unless you want to run it with a reverse flow - that is, the water comes up through the gravel and allows debris to be caught by other filters, rather than pulling down and trapping waste in the gravel. look into getting a canister filter in addition to the ones you already have.

I'm glad to hear you like changing water... I have 6 goldfish in a 55g, and change the water twice a week; keeps the nitrates below 5-10ppm. If I could, I'd do a daily water change, very therapeutic

On my 55g I have an Aquaclear 50, a Whisper 60 (came with the tank, not a fan of them), and now an Eheim 2217. I bought a used Aquaclear 110, but of course there isn't enough space between the tank and the wall to put it on, so I'm going to replace the AC50 with that when I move the tank in 2 months.

Aquaclears are excellent HOB filters, period. I'd recommend getting the largest one you can get/afford for your tank, because they do an awesome job. I cut a piece of foam and put it over the intake; this prefilter makes filter maintenance easy, as you mostly have to just wash the sponge out than the entire filter.

The Eheim 2217 is a pricey canister filter, but I am very pleased with it. Was on sale with all the media at the Big Al's near me, and you get what you pay for. The output was too intense for my goldfish though, so I had to angle the spraybar properly and, after some trial and error, my goldfish would venture to the other side

Check out the big aquaclear filters, you won't be disappointed. You can get two; jam one full of biomedia and the other with the standard foam/carbon/bio setup. And put your smaller filters on the tank for bacteria seeding and a little boost.

With goldfish, the more filtration and oxygenation the better. The only thing you gotta watch out for is too much current.

I went from a 5g, 10g, 20g, to a 55g with my black moors, after successive research and "OMG how did I stick 4 black moors in a 5g?!" It would have been so much cheaper to start with a 55g, but it would be too intimidating for a first tank.

Sounds like you've got a pretty good setup. I'd definitely pick up a canister filter and run them with your two Top Fin 30's on the tank. I like the Magnum 350's (relatively cheap and reliable) but there are several good makes. Look around there's no real big rush if the filters you currently have are handling the load. Get the python. With mine I do water changes while I watch T.V. or play computer games. You can find pretty good deals on 55 gallon tanks just shop around. Walmart has decent prices on tanks. It should run you a lot less than $500 bucks. I got my 125 setup for less than that even ordering a new filter for it.

Theres a 55 gallon package at Petsmart on sale for $109.99 I believe from $119.99.

Tank, hood, filter, heater, etc.