One of the things I would like to suggest is the idea of buying some high quality root tabs and grind them down into a fine powder. Litter it on the bottom of tank (especially where the planting is going to go) before moving your sand over. This will help jump start nutrients for any root feeders if you plan any. For the most part you'd probably be fine with just liquid fert. I've noticed a heavy water feeder like Water Wisteria seems to benefit from root tabs though (have an explosion of growth since adding one to where it's roots are).
If you are getting crypts...you are going to want to make use of root tabs. It's not that expensive when you consider how long a single tab can last.
The only other thing I can contribute is to be wary of the Water Sprite in a 20 gallon long. I had it in an old 20 gallon long set up and it was a hitch hiker with new plants. I ended up putting it's roots into my substrate and the thing grew taller than the tank was, curled over and then began growing out into the length of the tank. It was kind of neat but...it goes to show how it can and will outgrow the 20 long.
If you are getting crypts...you are going to want to make use of root tabs. It's not that expensive when you consider how long a single tab can last.
The only other thing I can contribute is to be wary of the Water Sprite in a 20 gallon long. I had it in an old 20 gallon long set up and it was a hitch hiker with new plants. I ended up putting it's roots into my substrate and the thing grew taller than the tank was, curled over and then began growing out into the length of the tank. It was kind of neat but...it goes to show how it can and will outgrow the 20 long.