If you haven't done it before, you are entering a new world. Since you used the word: "ecosystem", I would treat it as a new ecosystem. This means looking at the whole picture, not just a few details, such as; this plant, that plant, this nutrient, etc. Since you are not injecting CO2, I would strongly recommend making the investment in Diana Walstad's book: "Ecology of the Planted Aquarium." you will avoid many pitfalls and will move much more quickly up the learning curve once you digest this bible-of-the-low-tech-planted-tank.
As far as supplies, "That Fish Place" is certainly loaded with products (it's a big warehouse), although I don't recall how good their plant selection is. There are certainly many low-cost e-tailers, not least of which being the big A.