The answers to your questions are below between the carrots. HTH.
1. do seahorses need to be kept in a seahorse-only tank?
<Seahorses need to be kept in a species specific tank with the exception of a handful of safe seahorse tankmates.>
2. how often will a pair (or group) mate, and how many fry will there be?
<It depends on many factors but it could be as frequently as every 3 to 4 weeks. The number of fry depend on the species and age of the horses. Mustangs may range from 20 or 30 up to a few hundred, with the more average number being 80 or so in my experience. >
3. i dont really want to raise fry, but i dont want the seahorse to be alone as
i understand that they do better in groups. is there a way to keep more than
one without getting fry?
<You could keep all males or all females>
4. if i keep two males or two females, will they fight?
<No they should be just fine>
5. i have a tall 55 gallon reef tank with a false percula clown, a coral beauty
(dwarf angel), an arrow crab, a pink-tip haitian anemone, a brittle star, an
emerald crab, and various turbo snails and small hermit crabs. will any of
these not get along with the seahorse or be dangerous to it?
<The Coral Beauty, Arrow Crab and anemone would not be appropriate with the seahorse, but the rest of you tank inhabitants would be just fine>
6. i have a large refugium rock in a corner of my tank, will this be an ok
perch, or do they need something bigger?
<The rock should be just fine, as most will hitch to just about anything, but they do like branching types of décor.>
7. other than that, are there any general requirements that i need for the
<In addition to the regular equipment like filter, heater and such a skimmer would be highly recommended.>
thanks so much for your help!
<Your most welcome, Leslie>