10 gallons can be done, but only if you've previously owned them with some success in a tank around 5 gallons in size. The larger the tank, the harder it is for the dwarves to find food. They do not just sit there all the time until something comes and hits them in the snout, but baby brine shrimp are hard to see..in a large tank they'd have almost no chance. They sometimes do take frozen foods, but it's very rarely, and even so...they won't survive on it. To this date, only newborn baby brine shrimp are truly proven to sustain a healthy lifespan in a dwarf seahorse. Minced mysis, etc. has been tried, but they don't last long on it. Brine around 4 hours old provides all the nutrition they need, after about a day they loose almost 100 percent of their egg sack. and with it, most of their nutrition. If you were to feed them brine that's older, they would need to be enriched with selcon for about 2 hours, and stored in the fridge. Just remember, you WILL need around 3 brine hatcheries going set to hatch at different times. around 3 feedings per day, newborn brine, it can get overwhelming.
Can you keep pipefish with them? IMHO, only dwarf pugnose pipefish are suitable, other than that..they should never be mixed..especially with someone so new to them. Disease, outcompeting them for food, etc. It's just too much. Plus, 5 gallons is much too small for most species of pipes.
Starfish, skip it, hermit crabs..onyl certain types of the smallest species should be kept with them.
Temp, 75 degrees. Breeding, easily done, fry eat newborn brine also. In the long run, dwarves are basically like baby seahorses that never grow up. Can be kept with the adults, start eating and hitching right after birth.
Are dwarves active? Not really. Other seahorses are quite active at times despite what everyone says, but dwarves are delicate little things that fit the seahorse stereotype quite readily. Imagine a little tiny fish the size of your pinky hitched to a plant 75 percent of the day. They are cute little things..but may not be as active as you'd like them to be. Feeding time, etc. that's when they get moving.
Seahorse.org, the BEST place to start..it's one of the most frequently visited forums of mine that I go to
.