grow light fixture stand

How to set up Planted Aquarium?
Specs:
Lighting: standard, came with tank
Hood: standard, came with tank
Tank: 20 gallon; 24"L x 12"W x 16.5"T
Filter: AquaTech either 20-40 gallon or 30-60 gallon
Substrate: about 2-3" of black Gravel
I have an air pump/stick. Would I still need it?
I have a heater so I keep the tank at about 84F.
I keep guppies and I let them breed freely.
Would I need a CO2... thing? lol
Would I need a different substrate?
Where could I get a better lighting fixture?
All I want is a ground cover of grasses and some plants that would grow out of the gravel/substrate because guppies like densely planted areas so what type of plants would be recommended to me?
What would be the estimated cost of doing this?
Please don't send me a link, I've done research and I just can't stand the forums and other websites.
Thank you for your answers.
I did a very short write up with image on my experience in setting up a cheap and low tech planted tank for planted tank online community. If you want it I can e-mail it to you. Give me your e-mail.