A very good tank for them would be a 45 high. This would give them enough space all around. They need a tank that's close to 3 times or more the height of themselves. And like fluff said its all about how much dedicated you are to them. They require more care and need a lot of attention to all aspects including foods, tankmates, and water quality.
Brine shrimp isn't a good choice for a main food source. It's only a everyonce in a while snack. Its debatable about they're nutritional value, but from what we know when they aren't gut loaded theyre aren't very good as a staple diet. Seahorses that are raised on that food will most likely die of malnutrition. A better food source is mysis shrimp. An easily eaten food tat provides enough nutrition. But other foods should be used too. Adding selcon to whatever food they eat is a good idea too. The only seahorse that needs to be fed bbs are dwarf seahorses.
Im about to get a pair of seahorses pretty soon and IMO
the best thing you can do it exhaust yourself with research. Im writing an article on fishforums.com on basic care and all that so maybe that'll help alittle when it's finished.
I could write about these things for days but im just going to settle answering some of your questions.lol... Seahorses are only hard if you don't know what your doing