For lighting look for the right length and output, etc. http://shop.aquatraders.com/T5-High-...-Light-s/9.htm
As for the filter. You will want to at least mod it to have chaeto algae in it(or in the tank but it might take away the look0 and a 5500k CP bulb over it(not the tank).
Don't get carried away and do this all tomorrow take your time and spend your money wisely. I tried jumping in and lost alot of money...money that I could be using to have my 55 gallon tank up. So trust us when we say take your time. Have us help you plan it out.
We can help you turn the 20 gallon into a tank with a nice sump built in. I have a plan for a 20 gallon tank like that in mind(20 gallon long).