fantail goldfish will get a little big for that tank before too long... they are a great beginner fish, though because they're pretty tolerant of a wide range of water conditions.
Don't leave your lights on all the time. If you've got live plants, leave them on for a couple of hours a day (check out the plant forum as well....). If you have plastics or no plants, just turn on the lights when you feed or when you're actually watching the tank. Otherwise, you'll have algae, which is REALLY not fun....
I feed my goldie once a day, skip every third day. A day of fasting is good for them. They don't have a sense of "full" and will eat until they explode if you let them.... You'll have an ammonia problem if you keep feeding them that often (not flaming, just informing...).
As far as "cleaning crew" for your tank, the best solution would probably be a corydoras cat or two to eat leftovers, and maybe an apple snail to keep the walls of the tank clean. Chinese algae eater fish might also be an option. Unfortunately, even if you add a cleaning crew, your tank will still be far from maintainence-free. Nothing eats poo, you know...
Sorry to be the bearer of bad news, but if you want 4 fantails (or almost any goldfish for that matter), you'll need a much larger tank. They like to have 30 gallons for one, 10-15 for each additional one when they get bigger...the more water, the better. Bigger tanks and fewer fish mean less maintainence...I would suggest 55 gallons at least if you want that many.
Read up on cycling. There's a long post I added yesterday regarding cycling with fish that might help a little (letting you know about what to expect).
Goldfish are okay in a wide variety of temperatures, but do best in cooler water than tropical fish like. I keep mine at 72; room temperature....
It's really great that you're asking questions and wanting to learn. Welcome to the hobby! Ask as many questions as you can think of....we're here to help!
