It is sold in different grades Amazonia, Malya, and Africana.
The different types of Aqua Soil are not different grades, per se. The different varieties are more about different colors, and ever so slightly different in make up to the best of my knowledge.
which type of ADA AquaSoil should be used for a regular low maintenance 5 gallon fresh water set up consisting of low maintenance plants(java fern, java moss, hygrophilia, anubias, etc.,).
You could use any of the available varieties.
However, for the plants you are mentioning (ferns, moss, Anubias), I am not sure I see the point in using Aqua Soil....particularly when you consider the purchase to be "shelling out big bucks". In my experience, Aqua Soil is best suited for stem plants, swords, Cryptocorynes, plants that are "planted". There is no reason for Aqua Soil not to be used with the plants you mentioned (yes, I know you mentioned Hygrophilia
), but the properties that make Aqua Soil a unique substrate will kind of go to waste on the set up you have planned. Not saying it can't or shouldn't be done, just that for what you are setting up, your money is probably better spent on something else.
Also, does this stuff need to be capped with a layer of sand?
Absolutely not. Capping any larger grained substrate with sand or a smaller grained substrate is only going to be temporary. The finer particles will eventually settle beneath the larger ones.