one 10W6 sub in it designed to run between 250-300 watts. [ http://jlaudio.com/stealthbox/300zx_2seater.html ] I believe SGP racing is the only online place to buy them, otherwise must be purchased from authorized dealer. The stealthbox is designed specifically for the Z. In a coupe it mounts in the back left corner of the hatch and in a 2+2 in mounts in the same location but under the carpet. Also check classifieds for the custom boxes made for the coupe.
You should be fine with one sub and an amp to power it. Im not to sure about wattage, but make sure the amp matches the sub, and between 200 and 300 watts should be fine.