That 5gal tank would be perfect. The others would be WAY to big. There Dwarf seahorses. Not sure on the Real scientific name. There about 1" or so long. color varies as they seam to change depending on whats in the tank. I had white sand in the tank and they were more of a brown color but when i put black sand in the tank there more yellowish. Hatching Brine is easy. Just get a 2liter some brine eggs and an air pump and your good to go. I have 5 horses left but can order more. I have them on my site
www.SaltCritters.com