DO NOT GET 4 CLOWNS! 2 will pair off and kill the other 2. As for the firefish only get one species either the red or purple. Also, one gramma not 2, they are aggressive to conspecifics. If you want a tang, go for a kole and not a zebrasoma species.
As far as lighting, go on Amazon or eBay and get a marsaqua fixture, they are about $89 and are full spectrum dimmable LED. I keep tridacnid clams, nems, and all types of corals under these with no problems.
If you want to save yourself headaches and water quality issues, put a sump underneath it(40B) should do well. With saltwater you want volume. Skimmers are non negotiable, always get a skimmer rated for at least 1.5x-2x your actual volume especially if you want to stock heavily. When you make your sandbed make sure to have it at least 1.5" thick, preferable 2-3".