go big as u can. zebra's are shy pleco's. so def get lots of caves or driftwood for them to feel comfy. easy pleco's to keep in my opinion.if this isnt a show tank or using them to breed i wold suggest barebottom. or maybe painting the side and bottom of the tank black. more clean going barebottom. but a sand would be a nice choice if u decide not to go barebottoms. a nice school of small tetras would look nice aswell.