well i use an ehiem 1262 on my 50g cube. i could use a pump thats less powerful and be fine. somwhere around 600 gallons an hour should be fine. your main source of circulation will be done by powerheads like koralia, tunze, ecotech. depending on what you like.
just an fyi though it would probably be best to have something like an overflow box or something to cover up the hole you drill for the drain. basically what ever you choose you want to make sure little critters like snails or something can't get in and clog it.