Since you already have so much experience with reef tanks it might be a new challenge for you to try a different style of setup. I would look at a macro dominated system, or a non photosynthetic tank. It might give you a new direction to learn and create a greater appreciation/understanding of the hobby as a whole.
Seahorses can take any lighting, but the higher the light the more you will need to control the temperature. Most people need chillers to keep seahorse tanks at temps below 74.
For current design, I like to have a lot of flow in my horse tanks. The key is to break it up. Seahorses can't take jet stream style flows like the out puts of maxijets, they need there current to come from a wider area IME.
I run closed loops on spraybars behind my rocks to get rid of any chance of build up and to keep stray mysis from falling in, it works well for me.
If you have to have a powerhead a vortech on a constant setting with a cover has been used by many with success. Right now I have a koralia nano, I've used the tunze nanostreams as well.
Just leave a place for the seahorses to retreat to if need be.
Sand is a personal preference thing. Some people really like the look, but with certain species it is better to go barebottom IMO. It just depends on what species you plan on keeping. Whatever species you decide on, I would stick with just one since you are new to seahorses.
I prefer to keep 3x the height of the horse for vertical swimming room, so I don't go to deep on the sand.
Skimmers are cool, but IMO they belong in the sump and not on the side of the tank.
UV's are nice but if you run one use a prefilter and again factor in the added heat.
I really like refugiums on horse tanks because when the fuge is healthy it will feed the tank with larger pods that the seahorses will hunt, keeping them more active in the tank.
Cover intakes for powerheads or closed loops.
Buy aquacultured seahorses, from a place that raises the fry in a tank from the time it is released to the time it is sold. Buying TR or WC's will cost you more headache in the long run then the extra few dollars for an aquacultured horse.
If you don't plan on breeding, then get all the seahorses of the same sex. So many people are not intending to breed, but when the fry is released they do all they can to save them. Better to go with a same sex tank from the get go IMO.
HTH