Woah.. I would step back on that. If you really are not sure what you are doing..you just stepped into a possible nightmarish experiment. An experiment that tests your patience and your skills. DO NOT add any fish at all.... for about 2 months or so. I have tried similar experiments...but abandoned them cause the peat moss(soil is similar just more rotted) turned bad (black soil appearance after about 1 month) and poisoned the water so bad that algae blooms took over the tank. The water was green as kool-aid. Then I just ened up dumping the mess and restarting with laterite(I had two bags of it lying around--bought during a sale). BUT, big but here, many people have successfully grown in such a setup. I would say be very careful not to put plants up too often and mess up the water a lot. Get fast growers like hornwort or something similar to eat up the excess and keep algae at bay. You will NOT fail if you follow the advice of those who know. You may have to do a lot of water changes when algae appears.. some say not to.. but with such a small water column I would tend to do lots of changes. never vacuum the gravel EVER (at least for 5 months).. that may just stir up the mess under the gravel. It may work out just fine or it may be a HUGE hassle...either way you will learn something out of it..so its not a waste of time. I was just impatient with my 'mess' and my plants were dying becuase of the algae (not the other way around)..so I saw that I had to change it immediately. An inch and a half of soil seems like a lot.. but in nature it is more.. as long as you let it go it should be ok.. just test the water twice a week and get some cheap fast growers.
(I have a 5 gallon nano tank that is perfectly balanced (only one 10 watt CF bulb in it...) Im going to post pics of that tank as soon as it regrows again...(I picked about 30+ stems of saleable rotala indica out of it).
Help control the pet population...spay or neuter people won't spay or neuter their dogs or cats!