turning this 20 gal to reef?

I have some extra live rock. Id like to use this 20gal tank for a species tank or something. Would I have to drill this tank? A guy at my LFS said on a 20gal I wouldn't need a sump . Can anyone here tell me what Id need to make this into reef or just saltwater?

The guy said Id need a filter system ofcourse....just not a sump.

I'ma sump guy, but there are those here that don't use them. On my shrimp rearing tanks I just put a baffle and grate on the side and I have a filtre. 15cm deep sand bed and a foam block on top. I use an old Sander Piccolo skimmer and a small Hydor pump as a return.

what is a baffle and a grate? Im sorry..... I don't know what a foam block is either. What do you use for lighting and proper water pumps ?