Are you prepared for the dedication and work of a seahorse tank? It sounds like you haven't done much research yet, so are unaware of the amount of effort it takes. Not that I don't think that its not a noble endeavor to undertake, but be sure you know what you're getting into first.
This article covers the basics of getting started:
http://www.advancedaquarist.com/issues/dec2004/fishb.htm
There is also a pretty good video on setting up a seahorse tank:
http://www.youtube.com/watch?v=bbrBtKMZjGg
Finally, this is something I wrote as kind of a buyer's beware of things to think about BEFORE you start your seahorse tank.
http://www.fusedjaw.com/aquariumcare/10-things-you-should-know-about-keeping-seahorses-as-pets/
To answer your specific questions:
can i stock corals and seahorses?
Yes, but you have to ensure that they are not stinging corals. Most soft corals are acceptable.
how much flow?
You want a reasonable amount of flow, but you don't want the seahorses to get blown about. 5x to 10x turn over in a hour is good, but make sure you have some areas that are sheltered from the flow.
how much ligth?
Seahorses don't care about light, really, so you'd be basing it off of what looks good and what your corals or plants, if any, need.
what light fixture?
t5's or power compacts are best because they don't produce as much heat. You'll want to keep the temperature below 76 for tropical species.
any experience with seahorses?
Yes.
As I mentioned above, it takes dedication to keep seahorses. Also time, effort and money. But in my opinion, they're worth it. Research as much as you can, and be prepared to wait a good six months before even considering putting seahorses in your tank.
