Just wanted to add, I just recently came from your side too. A few things I would recommend
1. Use sand over crushed coral, there are many reasons the biggest would be that the crushed coral gets ugly and dirty easily and must be cleaned, and the sand will be able to host many micro and macro bioda that will help in creating a more natural filtration system for the tank
2. There is really no difference in freshwater and saltwater filtration as far as I know, though some will work better in fresh and some will work better in salt. For instance a protein skimmer is I belive the second most important piece of filtration, and you would almost never use one of these in a freshwater tank.
3. The first most important filtration system is NATURAL. This includes live rock, live sand, macro algae, and a clean up crew. Again this is my oppinion but I think most will agree with me here. I wont go into details on these things right now, but if you truely get lost dont be afraid to ask
4. Read. Even if you know EVERYTHING there is to know about freshwater, saltwater is all that and more. While not necesseceraly more work than a freshwater, it is defenitly more research.
5. I dont think a stingray will fit in that small of a system, but I dont know for sure. Once again read about that kind of fish, if a stingray is what you truely want, than prepare for that, I wouldnt go build the "basic saltwater tank" and then throw a stingray in. Most of the shark and ray family take a lot of special requrements. But like I said if that is what you REALLY want then go for it, there should be experience you can tap into.
6. welcome to the forums and the experience, feel free to tap. There are other forums out there with more users even, but after being involved with about 4 this one has become my main one, the people on it are friendly, quick to respond, and over all willing to go out of there way to help, and that after all is what makes a forum, the people.
I could tell you a lot more do's and dont's but I will leave that for you to read up on, but make sure you know them before you start, it WILL save you money.
Just wanted to make this clear this is only MY oppinion, in this hobby you will find that everyone has their own. And its definetly not cut and dry which is the best way to do things. I got a quote that I like that goes like this "The only thing I have seen that has completly destroyed a tank is leaving it with no water for a while, if you do this nothing lives"