Smoke whatever size you need to feed the crowd. I've done hams from 8 lbs up to 20+ lbs and they come out great. If you need a bigger one and have access to Restaurant Depot, they have great hams. You can also get smaller hams (I prefer the 'butt' portion) at your local grocery store.
I do mine at 325 and it takes about 20 minutes per pound to get a fully cooked ham up to 140+ degrees. I usually glaze near the end of the cook.