Hi
Seahorses (SH) are beautiful fish and if you have the time, money and dedication to them you will not be disappointed. Fish keeping experience is useful, but not necessary as long as you do lots and lots of research, take it slowly and ask for help if unsure from experienced keepers.
If you like the standard species (kuda, reidi) TMC and your LFS will likely do them, if you are after more exotic/ uncommon species a specialist shop is better. Never buy online unless you know/trust the seller. It is reconmended that before you buy SH you observe them for physical signs of ill health/ damage to their skin, check body mass and make sure they feed them infront of you so you can make sure they are eating. SH's can go down hill very fast very quickly so it is important to check them over before buying. (i travelled 9hrs round trip to see mine before i brought them)
As Tina said make sure you get captive breed SH as they are endangered and are already feeding on frozen foods.
As already mentioned they require a species only tank with special requirements such as : for most species a minium of 100L is required (allowing approx 30L per pair), Low flow (as high flow can stress them out and stress is one of the biggest killers of SH), Low light levels as SH have very sensitive eyes and if the light is too bright it can damage their eyes and they will hide, a tall tank as SH swim vertically not horizontally like normal fish, plenty of hiding/ hitching posts - macro algaes are great for this, it's sound silly but the more places they can hide the more likely you are to see them out and about as they feel safe. You will also need to feed them 2-3 times a day (if they eat frozen food you shouldn't feed them live food as they will go off the frozen), and be careful on what tank mates you have.
I'm not claiming to be an expert but i am one of only a few people on this forum with SH's so if you have any other Q's or need any help I'm more than willing to help. If your interest a link to my journal is below.
Kelwoo