as far as skimmers go.. i can say, from experience now, spend the money now and get a good one..
i made the mistake of trying to do it cheap, got a visi-jet and its useless. i should have spent the extra few bucks on a good one and now i wasted the money and still got to spend the extra.
be careful on ebay too, a lot of junk floating around (no pun intended), unknown brands and a lot of drop shipped discontinued models claiming false claims and cheap prices. best thing to do is research, find one you like, or take advice from people here, then once you have found a few you think will be good, then see if you can find them on ebay or craigslist etc cheaper, im not an expert on them really, as far as what works, but i have seen good reviews about red sea skimmers..but im sure others will have better ideas...
and the carbon, i use activated carbon in all my tanks, and has positive results. but you do need to change it, often. i actually went to petsmart and bought a box of cheap small filter cartridges, think they were actually for a small penguin
HOB filter. then just put them in the sump loose, below the filter pads. they have carbon inside the filters and easier to change than emptying bags and so forth. just take them out and throw in new. rinse them first though, else get carbon dust come out of them and looks dirty for a while...
also have live sand in my sump, but if you dont have baffles then dont do this, else your pump will suck it all up and go bang...