I have a 70 gal tank, a fluval (505, I think --- I'm out of town now so I'll
have to look it up later if it matters), a powerhead, and heater. Plus I
have an automatic feeder that plugs into an air pump to keep the flakes dry.
The light is on a timer. The feeder is only really for when I travel, but I
gotten used to relying on it, and the fish know what that sound means twice
a day!

I currently have just 2 fish, a blenny and a clown + 2 hermit crabs. I'll be
getting another clown soon. I make sure there is pleny of rock and broken
shells for the blenny to hide in ( he sleeps between the heater and the
glass! ) I'll probably get another 1-3 more fish sometime. I had a 2nd
clown, but he caught some kind of disease and treatment did no good. (A word
of advice, go ahead and get a small 2nd tank for a hospital tank!)

I probably only change the water about every 6 weeks. I use Amquel to treat
the tap water. I use carbon in a bag in one fluval basket, some ammonia
soaking resin in another basket, and keep the 3rd basket for bio-filtering.
I use Coral Life salt in a 50lb bucket.

Anyway, it is about as "self-sufficient" as you can get, I suppose. I keep a
good watch on the ammonia and the salt level (with a Deep Six tester). I've
had very few problems --- the worst being when the first Fluval burned up on
me. I sent them the powerhead and they replaced it with no questions asked.
I made do with a small bio-wheel until I got the new Fluval.

The hermets take care of a lot of the janitorial duties. Every now and then
I provide them with bigger shells as they grow.

I initially bought a testing kit that tests just about everything you test
for. But about the only thing I still test frequently is for ammonia, and I
never have any problem with it.

I top off the water to bring the salt level down to normal now and then.
When I do change the water, I move all fish + crabs into a bucket so I don't
damage or stress them out. And I make sure to suck up the detrius when I
change the water, by stirring up the sand vigorously while I siphon the
water out.

I've been doing this for over 4 years now, and the tank has worked out just
fine. I've had the clown fish for the entire time. Worthy of notice is that
I don't have any live coral in the tank, and the hermits are about as hardy
as any tank critter gets ! A medium sized resin fake barnacle provides some
color and a comfortable hiding place for the blenny.

This is just my experience. If you add any other invertibrates like coral or
anything else, I'm sure maintenance and attention to water quality would be
more of an issue. But with just a few fish, lots of horizontal swimming
room, and a couple of hermit crabs, I have had very little trouble. The only
thing I really have to worry about is the power going out for more than a
day --- but you can get pumps that run on battery when AC goes off or even a
UPS (Uninterruptible Power Supply) to take care of that.

Hope that helps!

P.S. I agree on reading the links mentioned in this thread!