jjI have several self-supporting tanks where I don't even need to feed the fish.
When creating an ecosystem you need a source of constant nutrients to fuel the plants and micro algae and light. From there on its basically a matter of adding the right number (and kind) of fish for the amount of food that is produced by the tank.
What I did:
For my 125g tank, I added an inch and a half of low-nutrient topping soil with a 1-1.5" thick cap of blasting sand (in retrospect I would have used something else since I think my batch is leaching chemicals into the water) for the nutrient base. From there I added 4x96w of PC lighting (set on a timer 8 hrs continual light).
This soil layer was chosen because it will hold nutrients for several years that the plants can use without having to add dry compound fertilizers. Additionally the sand cap prevents too many nutrients (primarily NH4) from leaching out into the water column - limiting algae growth.
I have a 15# CO2 cylinder attached to an in-line CO2 reactor (i chose this one over the other kinds because it needs the least cleaning/maintenance of the diffusers/reactors while still having a high rate of efficiency). The CO2 is imperative IMO, and if you skimp on it your plants will have a more difficult time getting established and growing leading to algae problems. 15# will probably last 1-2 years at 4 bubbles/sec.
From there I stocked the tank heavily with wood and stem plants, different foreground plants and lots of slow growing java/anubias. I think a good fast growing foreground plant like glosso (or dense one like HC) is pretty important to this kind of tank since it will soak up nutrients from the substrate as they leach into the water preventing excess in the water column.
As for fish... If you don't plan on feeding the fish at all, I would suggest small fish like live bearers or
kribs/apistos and of course any sort of algae eater you like (ottos/bristlenose are my favorites). The live bearers will regulate their own populations depending on the food in the tank so you won't have to feel bad about not feeding them. Shrimp are also an excellent choice, particularly bamboo shrimp since a soil tank has plenty of microscopic partials of debris that they can feed on.
I wouldn't skimp on the filters though, not that you need them to scrub the water with carbon, but you will need to circulate the water so it doesn't become stagnant and cause problems.
Also MTS are vital for a soil tank as they turn over the soil and keep it oxygenated.
So far my tank has been running wonderfully without any sort of maintenance other than topping up the water and trimming for the past year.
Another beautiful thing about this sort of self-sufficient tank is that you won't have to do frequent water changes since not that many nutrients get leached into the water/any that are are sucked up by the anubias/java fern on the wood. Organic build up is eaten by the bamboo shrimp and guppies off the surface of the water and recycled so that it doesn't have a chance to build up that much.
As a side note: This sort of system also works w/ non-soil tanks, but you need auto-dosers and a lower fish load.