i would say dont use any substrate, they are VERY messy critters and it makes cleaning so much easier if they have no substrate...
Keeps your water cleaner longer and you can see all the poop easily, also they are VERY messy eaters...
I reccomend a good filter, and you dont need to fill the tank to the top as they dont really swim in the upper layers, this allows for mayby a smaller filter but you are acctually over filtering which is always good...
DONT keep with goldfish!!!! goldfish nip at them...
They are wicked pets... i would say a 3ft tank would be perfect for them.