Unless you jam with other instrumentalists on a regular basis, a resonator should be unnecessary. My S.S.Stewart is noisey enough without one and most often I stick a dish cloth in to further dampen the sound. If the banjo in question lacks an arm rest, you might consider getting one to save wear and tear on your arm (resting the arm on the rim can do real damage, to the arm, if you're playing for any prolonged time). I would also recommend a substantial hardshell case if you "fly" between gigs.

Good luck!
Charley Noble