hi there. there is not really an "ideal" sealed enclosure size for any driver. there are advantages and drawbacks to both large and small.
3 cubic feet, net, sealed for that driver is fine.
here are some different configurations (2, 3, and 4 cubic feet sealed, and a 4 cubic foot ported with 22hz tuning).
if you have a medium size room, you will get some natural boost starting around 25-30hz, so the sealed won't roll off as fast as in the model.
the model is for one sub and one watt.
bottom line: if you want to use a sealed, 3 cubic feet is fine, as you don't gain much by going larger.
edit: and for an amp, something around 300-500 watts per driver would be good. if you go with a higher powered amp, you might damage your driver with sub bass tracks. two of your sealed subs will actually get pretty loud with that much power.