Sorry in advance for the long story.....
Having kept many seahorses over the years, under different situations, the most important thing is getting your seahorse to eat frozen mysis. If its stuck on live food, then you are probably going to lose them whether in a species or community tank. If you keep them with other fish, they like small, slow moving fish that won't gobble up all the food before they get to it. In general, seahorses are very slow eaters; although, mine seem to be the exception to the rule. My original male, when he was only 4 inches, would suck up a floating mysis before my elongate tang (think sohol or clown but with blue colouration) could gulp it down. Really funny to watch the tang trying to figure out where his snack went.
However, if you wish to breed them, get them their own tank because everything else seem to thick baby seahorses are just the perfect little appies.
Mine are now in a 33 g with cleaner/peppermint shrimps & an Indonesian purple tang (a Kole tang without the stripes or eye-ring) who will soon be leaving.
All this is moot because unless you are willing to buy 12 or more at a time, your LFS won't bring in seahorses since there is now a CITES ban on their open importation. They would have to pay a license fee to import them & you'd have to put up the money upfront for the doz. or so seahorses for most LFS to consider it.
When I get a bigger tank (200+g plexi) for my fish, I plan to convert my 100g into a Seahorse Ranch
If you're gonna dream, dream big & expensive
My LFS will bring in my doz. for me, but it'll be a big dent on the VISA
PM me if you want me to contact you when I do this (won't be for a few months).