Sounds like you are getting great advice, but check out seahorse.org for even more in depth information.
Types of horses: I recommend H. Erectus. They seem to be rather hardy and I have been told the young are easier to raise. I haven't had much luck yet myself, but perhaps the next batch will work out.
I have not found seahorses difficult to keep, but the difficulty comes when raising the babies and treating diseases. In addition to your tankmates not being compatible, the reef system/fish would likely have pathogens that could hurt them as well.
Getting seahorses is a great excuse for setting up a new tank. ;) A seahorse setup is MUCH cheaper than setting up a reef tank b/c you don't need the expensive lights or a lot of sand or additives, etc. You DO need a good filter b/c they are pretty messy.
I love my seahorse tank! It is 18" long x 18" wide x 32" tall. I think it is a perfect tank for horses. They seem to really like swimming up and down in it. The breeding display is beautiful in this tank. I am actually wanting to make it an algae display tank as well. So, I guess I will need to upgrade the lights a little. There are some beautiful algaes out there that rival corals in my opinion.
The moment his HEAD is in view, hit it with the LIVE ROCK!