The amount of live rock isn't really a factor at all, and no, they do not hurt themselves on it.
Btw, you don't EVER buy wild caughts. Not only do you have a part in depleting wild populations (which isn't needed since there are hundreds of breeding projects out there), but you'd also be buying something that would cost a fortune to feed- and has an almost 90 percent more risk of getting a disease than captive bred.
As for buying from Dracomarine, good job! They are one of the very few seahorse breeders that supply healthy stock and know what they are doing. Seahorsesource (the choice place to buy a seahorse) is also worth looking into. If you want a great beginner species, try Erectus
. You may be able to fit around 3-4 in a 30 gallon, but it would be best off by sticking with two to begin with. (stocking suggestion is for erectus only, some other species show variability) Make sure you also have a quarantine tank up beforehand. You really don't have an idea of how bad and complicated seahorse diseases can be :p.
As for the whole skimmer debate, there really isn't much conclusive data that says skimmers cause internal or external gas bubble disease. The micro bubbles are of some concern, but more so for male seahorses. The bubbles get caught in the pouch- leading to pouch emphysema is some cases. In some scenarios, skimmers are THOUGHT to be what causes it, but there are so many things that could have been the cause. Oversaturation of gases in the water, bacterial infections, etc. If your worried about gas bubble disease, look into Diamox (a pill for humans that causes bloating, etc. to go down with gas bubble disease).
As for getting the "pods
" to breed, you mainly want amphipods (seahorses love these), copepods are also eaten by some individuals but very rarely.
Lastly, like said, DO NOT mix different species, and DO NOT mix seahorses with pipefish.
Hope that helps a bit Melosu, just remember, everyone on seahorse.org is always willing to help if you need it! Good luck with your new project, seahorses are my passion for obvious reasons!