Tom,
Slow down a bit. Dwarf seahorses are not a good beginner seahorse. They require constant hatching and feeding of live brine shrimp. The brine shrimp need to be fed immediately after hatching or else they need to be enriched for at least an 8 hour period prior to feeding them to the horses.
Small tanks are very difficult to keep stable water parameters in, especially with dwarfs in them. They require a very high feeding density as they don't hunt for their food but rather wait for it to float by. And I can tell you that 3 pairs in a tank that size is going to require a huge amount of food to make sure they are getting enough to eat. In a tank that size you can get by with at least 6-8 pairs of horses. Dwarfs are a maximum adult size of 1 inch from tip of tail to top of head.
You will need to feed at least 2-3 times a day and do water changes daily and remove any uneaten food an hour after feeding.
2-3 brine shrimp hatcheries, plus another 1-2 containers for enriching the brine in.
You can not use live rock and live sand from an already established tank because you will introduce hydroids into your tank which will kill the dwarfs. The only treatment for hydroids is Panacur which inturn will render your system uninhabitable to any algae eating critter and most corals. The effects will last at least a few years even with running carbon and doing water changes.
I would reccomend you check out either eahorse.org or syngnathid.org, both are sites dedicated to just seahorses and they both have forums dealing just with dwarfs seahorses.
BTW, dwarfs and pygmies are 2 totally different species. Dwarfs are Hippocampus zosterae and pygmies are Hippocampus barbiganti.
