Seahorse tanks? 10 points to good answer?

i'm going to buy a seahorse tank to put 2 or 4 seahorses i already did extensive research but i want to ask others how big does the tank have to be and how many gallons and what other things do i put in filter type and how many is a ground filter� and one that releases water from the top okay can i put in artificial coral and what plants do i put in also do i use sand or pebbles and what else do i put in the tank