hi valerie. i'm in the same boat as you... althouh my tank is 35G
from what i've learnt if you want coral, or invertabre. they require a very powerful light souce, and a powerhead or skimmer for water movement.
in my tank i'm looking at seting up clowns. with LR
if you do water changes weekly you probably dont need a protein skimmer.
what substrate will you be using? live sand? coral sand?
you will need a heater.. 100-150W should do the job.
i cant recomment any lighting. as i'm new to this too. it;s not cheap thats all i know