I would get as big of a sump as you can. More water, more space, better stability. Acrylic is the best material for sumps IMO, and any used fish tank will do as long as it fits. You don't need a customer built sump, just a box that holds water and your equipment. I am using an acrylic 60g for my sump, and it has plenty of room for evap, and holding the overflow water from the tank if the power goes out.