As far as lighting, look into a 4 bulb t5 fixture. Ive been using a 4 bulb on my 20 long for over a year and currently have a RBTA, im also had 2 condies that where in ther about 6 months before i sold them. The 4 bulb t5 is perfect light for a 20long. No need for the penetration of halides since the tank is only 10" from surface to sandbed. A halide would cook the tank and probably melt some corals.
I used a 4 bulb 30" 96w Current Sundial T5HO. Cost was about 300 when i bought it. Another option is leds. A A250 kessil will light the tank perfect too for about $250.