The only horses you can keep in a ten gallon are dwarf seahorses. Unfortunately, these are probably the hardest to care for. But not impossible!
You're going to want less flow than in a reef tank because they are not strong swimmers. Nothing in it that stings like coral or anemones. Seahorse tanks are the only place I recommend fake plants. Lol
But some pretty macro algae is even better. They will need frequent feeding because they pretty much swallow straight into the intestine. No stomach for storing food. At least twice daily. I'd set up a brine shrimp hatchery so you can always have newly hatched (after a few days they lose their nutritional value) available. It would also be good to add a bottle or pouch of copepods every few weeks.
I wouldn't keep any other fish with them, but maybe some sexy shrimp (someone else weigh in on that please). To avoid accidentally adding colonial hydroids, I'd use only base rock and simply seed with some bottled bacteria. A good clean up crew is a must because they are messy eaters. I'd stick to snails though.
Any more specific questions? That's all that comes to mind right away.
Someone stop me! Please! But... not just yet...
55 Gal Tropical FW
55 Gal Mixed Reef