:drooling: That's a nice setup matpat. I'm slowly whittling away my wife on the idea of a rack of tanks in our computer room.
10g tanks are great for planted tanks in my opinion, they are a little small so you have to keep up on mantinance but otherwise they're cheap to setup and cheap to stock. You have several options for substrate depending on how much you want to spend, but before making that decision it's important to know what your goals are.
Most important is how much light will you have? I've got a 10g setup right now with 2 16watt spiral compact fluorescent bulbs in a DIY canopy. It's a lot of light for such a small tank, the 2 watts per gallon rule doesn't necessarily apply to small tanks, usually you need a little more. Spiral compact bulbs are rumored to be inefficient due to "restrike" although I've never seen it actually measured, the suggested method for calculating actual watts per gallon when using spiral bulbs is to devide the rated wattage by 2 then devide by gallons. I think that convention is incorrect because my plants and algae behave as if I've got much more light. I'm rambling and it has nothing to do with substrate...
If you've got roughly 25 watts of 6500k lighting over a 10 gallon tank you should be able to grow any plants you want, you will need fertilizers and CO2 though or else you will grow a lot of algae. DIY CO2 is easy to build and pretty effective on a small 10g tank, for a few pennies a month there really isn't much reason not to do it, unless you just don't want the hassle. The benefit of CO2 is that it can help control agae and will help your plants grow faster. If you are adding CO2 and have high enough light to benefit from it your plants will grow and to grow they will consume nutrients which means you'll need to add fertilizers. If you are adding fertilizer (nitrogen, potassium and phosphate would be the most important, they are not contained in sufficient quantities in most all in one liquid fertilizers, you'll need seperate bottles for each) the plants will get all the nutrients from the water so your choice of substrate isn't very important. I've got inert playsand in the tank I mention above.
A nutrient rich substrate is advantageous when you grow rooting plants like cryptocornes, sword plants or valisineria. Any of the commercial planted tank substrates will work, ADA Aquasoil is supposed to be the best, but it's also the most expensive, laterite, flourite, eco-complete, soilmaster, etc are all good substrates, some having specific strengths or weeknesses but generally they are all better than plain sand. The root feeders will benefit from these substrates but stem plants, floating plants, rhizome plants and mosses won't benefit much, they'll still need water column fertilization.
It's a tough decision to make, if you want the lowest mantinance tank possible I'd suggest using a plant specific substrate and use about 20watts of light over the tank for 8-10 hrs per day. Plant root feeding plants that are hardy such as cryptocornes and swords and add some anubias or java fern to cover rocks or driftwood and you'll have a good looking tank that doesn't need much more than the occasional water change and light filtration. If you want to keep faster growing species of plants such as stem plants or floating plants I'd bump up the lighting a little bit (not because the plants need it but it does help reduce the probability of dead plants) add DIY CO2 and fertilizers, you can use whatever substrate you like, from gravel to a high end substrate like aquasoil.
I'm experimenting with a new setup that uses a few inches of garden soil (dug from my back yard) covered with an inch of gravel. Search google for Diane Walstead or natural plant tank and you'll find a lot of information. I'm planning on about 20 watts of light on this tank, I think I'm going to plant vallisneria, cryptocorynes and I'm going to try to find some aponogetons to fill it out. I haven't gotten far with this setup so I'm hesitant to recommend it but several people have had a lot of success using a soil substrate.