Great place to start is here with the Stickies.
http://www.reefcentral.com/forums/showthread.php?t=1031074
If you already have a 220, then roll with it. A 220 would give you lots of fish options, which most importantly, build your tank around the primary fish (and possibly coral) you want to have.
Tangs and other larger fish for instance need 4' long tanks or more depending on the species.
I run a 150 gallon tank (5" x 2") with a 35 gallon sump. Read everything here for like 2 years before starting and still come back with questions from time to time.
The only thing that may be more time consuming is water changes (dont' know, never had freshwater fish). It would be good to set up a saltwater mixing station that can provide you with 10 - 20% each week of your tank volume.
Also, you could look into the Triton method which attempts to avoid water changes via nutrient and mineral supplements through a large sump/refugium, but I have no experience with it.
Lastly, take your time. As many will tell you, nothing happens fast in the saltwater hobby. Go slow, research, and don't jump ahead and you'll avoid most mistakes others make.
Oh, and do not reuse the gravel. You want more of a argonite sand, 1 to 2" deep unless you want specific critters that demand deeper beds. Some people go entirely bare bottom as well. Sand beds are preference and specie specific demands, so long as you've accounted for your bioload.
Gravel allows for too much pore spacing and less surface area, which leads it to be more of a problem than helpful.
