I have 5 gln hex tank with sand, before I filled it up, I had about a gln of water in it and just simply used my fingures to plant the foliage into the sand.
I do not have my tanks cramed packed with plants either. Most eco systems have patches of plant pockets with rocks and eddies, open beaches and so forth. I use to go diving into the lakes I lived on as a kid and made mental notes on just how the plants grew in the water.
As far as planting in the sand, its just like a rice paddy, use your fingers and push the plants no more then an 1/8 inch into the media after the roots. And for your fertilizer, if you want to get the tank cooking fast, add some pellets under the sand and they will disolve over time. Once your tank is balanced and growing the fish will be able to deal with the growth.
You can use peat as a first layer and then place the sand over the top, lakes are usually at a natural state like this. As the weather storms accross the surface of a lake, the wave action does churn the bottoms like the surf of the ocean. Causing the bottom to layer up with run-off and sediment build ups. Thus creating sand beaches all over the effected areas of the lakes and ponds. All lake bottoms have several layers of peat, sand, peat, sand, gravel layers from years of evolution. If you live in an area that affords you several lakes and small bodies of water, take the time to go and do some under water exploring. Do a case study of your local aquatic eco systems. You will be amazed at how each body of water differes from one another. Thus, you will have a greater visual picture of a true eco system whe it comes to the substrates. Have fun getting wet......8>) Maximo