You can sometimes find MTS as "pest" snails at your lfs. I got two for free from a lfs and they've reproduced to populate 3 tanks. They are a long cone shaped snail with a trap door. They are noctournal and burrow in the substrate during the day. I believe each snail is both male and female, so when they mate, both snails will lay eggs, so you only "need" to start with 2. Also, if you plan to plant your tank, the plant roots will help with those gas pockets as well.
As for lighting, that is it's own monster. There's SO much info about lighting, but basically you have to have enough of the right kind of light to get your plants to grow, but not so much that you create an algae farm. Light has to be balanced with other nutrients including fertilizers and CO2 dissolved in the water. So the level of light you choose should be determined by first asking yourself how much work you want to do and how much money you want to spend. High light means you probably have to buy a very expensive CO2 injection system, and on a tank that large, you'd want a 5 pound CO2 tank or larger. You'd also have to dose fertilizers regularly. If you wanted low light, your plants will grow much more slowly, but there will be very little extra cost or maintenance involved.
I'd for sure reccomend T5HO lighting, as with a tank of that size and depth, you need the penetration that they will provide, unless you want to take the plunge into LED's.