rookie sump questions

[Snappy]

I am now at the stage where I need to add a sump to my 130 gallon. My tank has an overflow box and is drilled for that application. I want to plumb it for an over the glass return and want to hook up my 30 gal refugem/species tank in line with the same system for my 130. Any suggestions? I have some room underneath the main tank for the sump but am at a bit of a loss on how to proceed. I only have room for a sump about 18" x 36" x 24". Is that big enough? What is the best medium? Live sand with a live rock or two? Add in some baffles? I do also want to put my skimmer in there? Should it have a light? Glass tank or plastic tub? etc.
Thanks,