Did somebody call??
Good advice and suggestions thusfar.
Seahorses can be very rewarding, and very time consuming and very heartbreaking. I had a great pair of wild caught Brazillians that spawned every other Sunday for a long time - remember the early AM rattling brine pots?
The good news is that there are several species of horse that are readily available tank-raised - although I'm having some blips with supply, ORA carries H. kuda and (sometimes) H. procerus. These are pre-trained to eat frozen Mysis shrimp, makes life a lot easier. I've weaned wild caughts onto Mysis too but depending on the individual, it can be tricky. Seahorses are "vulernable" (as opposed to endangered) and they've been added to the CITES appendix, so trade in them is currently being monitored. I'd strongly encourage people to buy captive propagated specimens when at all possible.
Flow - you'd be surprised at how much fun they have "playing" in the current but they can't tolerate fast moving current. They need places to hold on with their tail ("holdfasts") and I use caulerpa, sponges and sometimes artificial plants - the colourful artificial plants can inspire colours in your horses

They can and do change colours at will.
Pipefishes are readily available, although I do not know of any commercial breeders of these, I have had some gulf pipefish reproduce and I had some success rearing them, to the age where I gave some to a friend.... but I don't know if there would be a demand for them.
Live foods: brine, ghost shrimp and the like, live mysids and frozen mysids. Size of foods depends on the size of the horses, but most can eat the Mysis, except dwarf seahorses (H. zostrae) which must eat live brine, baby brine and I've had some success getting them to eat Zooplex (Kent) and Cyclop-Eeze (Argent Labs)
Hope this helps,
Jenn