Once you go saltwater, you'll never do fresh again.......
It's not that hard to keep salt fish only, typically the fish are 3-4X more expensive than fresh, and all you need to do is add the synthetic salt mix. If you can keep a fresh water tank alive, you can keep a fish only salt tank alive.
For any tank, I'd recommend a 55 gallon minimun, the smaller tanks below 30-35 gallons just fluctuate too much and turn into actually more work than a bigger more stable tank.
I've gone hardcore the last 10 years and have kept a 135 reef with hard and soft corals, aquaculturing them and trading coral frags with other reefers.
Trust me, a reef tank makes porsche parts look almost cheap.......almost.
Heavy duty lighting, protien skimmers, live rock, and lots of patience. The more I leave it alone the better it does, most people yank their water chemistry around always searching for a magic bullet or pill to solve their problems, read read and read some more.
good reef tank sites at
www.reeffrontiers.com
www.reefcentral.com
If anyone has salt water tank questions, PM me and would be glad to make suggestions.