I think I can answer one question and comment on another: water changes are not needed to cycle a heavily planted tank. The plants consume the ammonia as fast as it shows up in a heavily planted tank, so you don't have to worry about cycling the tank at all. But, if you use ADA aquasoil as a substrate it pays to do some water changes in the beginning because that substrate releases a lot of ammonia into the water initially.

The comment is: we very rarely will have a non-light limited tank. In fact it is likely that all of our tanks are light limited. Sunlight is far more intense than our best lights. Our goal it to make sure it is always the light that is the limiting factor in plant growth, not a nutrient. However, having the same conditions in the tank day after day is more important than having CO2 be non-limiting, as far as algae is concerned. Algae are more likely to start growing as a result of changes in tank conditions than as a result of a constant tank condition. That is how I interpret what I have been reading here for several months now.