You do not need a sump, although I like them because you can hide all the other equipment.
I like my remora. There is a huge debate on protein skimmers and seahorses. IMO a skimmer should only be kept in a sump, I am not a big fan personally. I like to use refugiums for nutrient export and pod production. JMO
Keeping corals is cool. I love them. I like to give my horse a very nice home to live in and me great stuff all over to hitch on. Keep to the seahorse safe corals. Mainly softies with no sting. Leathers are good. My horses favorite hitch now is the macro algae and the tonga branch rock. Before the sump he really liked the filter intake, the thermometer, and the heater. Goes to show a horse will hitch to anything.
My tank is a 65g acrylic with a homemade cutom built in overflow box. I have a 20g refugium under the tank filled with 4 macro algaes and 30lbs of lr. For filtration I use a fluval 304, and an 18 UV ( kinda over kill, get it over kill

). My return from the sump is from a Mag5 which is split into two before coming into the tank.
The display has a 2" sandbed mixed with carbi live sand and crushed coral. There is a little over 100lbs of lr. I have a LR support structure/spraybar which has a Mag 3 attached.
I have 1 reidi seahorse which I got as a WC back in 01. He is at least 6-7 years old. I also have a dragonet goby which I've kept for three years. A yellow watchman goby which has been with me for about 6 months. A diamond goby I've had for a couple of months. A sixline wrasse whose been around for 8 months or so. My newest fish is a lawn mower blenny whose been with me for about two hours.
For corals I have 3 different leathers, 6 different zoa's, 9 different species of mushrooms, some green center clove polyps, random hitchiker fan worms (feather dusters you call them) and some xenia.
My clean up crew is about 35 snails ( nassarius, astrea), 15 scarlet reef hermits, 1 cleaner shrimp ( I don't recommend you get one) and I think I have 6 peppermints left. I a pod or two thousand, and a bristleworm or ten.
Honestly if you understand how to setup a seahorse tank I think there about a 2 on a scale of 1-10. I know I have been lucky, but a seahorse was my first fish I didn't win at a carnival with a ping pong ball. I knew nothing then, I know a little bit now.
If you buy a good CB seahorse you can feed it frozen food. I was ignorant and bought a WC that has never taken to frozen food so I have to feed live fresh water ghost shrimp. PITA and it is expenive compared to frozen. I spend over $600 a year to feed the one horse. Feeding frozen you'll spend around $50 or so. The price of a good Cb is well worth it in the long run. I do breed mysids, but not enough to sustain a seahorse.
Check out seahorsesource.com they have great horses at very repectable prices. I'd love to get some brevies, but I don't have the room or the chiller.
Oh gemini, your Welcome

There's alot of good seahorse forums out there.