The only filtration difference really is that the tanks get messier since they're lazy eaters and you're feeding a bit more often. So, good filtration is a must, but there's no specific filtration required. Lighting doesn't matter. Seahorses don't really require lighting and I'd be more concerned with having too much vs too little. People use T5's all the time though.
Circulation has several schools of thought. A lot of the older sites said low flow but most people have found that they can handle a lot more than people give them credit for. I'd say to keep the flow low-medium with at least some areas on the low side so they can relax (not sure the magic number these days, someone else might know). On my tank I have two vortech mp10's but they're set to almost the lowest setting. At that setting they pump out less flow each than a Koralia nano (~225 vs 450ish) so they don't push the horses too much since I have 2 of them they give me an even flow throughout. A bit overkill but it works. I'd do more than just a hang on skimmer will provide though, if for no other reason to get the filtration going. Also, put a fish guard on any powerheads. They've been known to put their tails in those things.
