Hey there,
When you first add sand...it will take a few days to settle down. The bacteria in your tank will pull it down to the bottom. Have you started the cycle in your tank?
As for lighting, you probably have a plain ole' flourescent light...which will be insufficient if you plan on keeping any corals in your tank. If you just want some fish, that lighting would be fine. You might want to look into what you would like to put in your tank in the future...such as corals. Some need intense lighting such as a Metal Halide bulb...and some dont need much light, such as PC or VHO lighting. Thats up to you...but my best advice to you would to get the best lighting right now that you can afford. Trust me, later down the road you will be thankful.
The mechanical filter will help keep your water clean...but you should look into getting a protein skimmer, especially if you want to keep a reef tank.
Good luck on getting things going....just take your time...dont rush things!
HTH
stapler