Hi,
The 1000 or 2000 would b ejust fine for a 70g system. We are expecting our first shipment of them in here next Wed / Thurs.
As far as the return pump goes, I would recommend something around 500gph. Take a look at the new Maxi-jet Utility pumps, as well as the smaller Tunze silence pumps. Both of these can be ran internal or external, very low power consumption, and extremely quiet!
Thanks,
Jeremy