1. Will the mountain be crowded or will I be completely alone and kicking out the snow in Dec?
The standard route climbs through a ski resort. If you have good weather and conditions, I doubt you will be alone.
2. Do I need to be roped on a South Route attempt? I've gotten mixed reviews from different climbers and while I'm not planning on it, let me know if this is a bad plan.
I have never been roped while climbing or descending the South Side.
3. Aside from the normal preparations for a winter/alpine ascent, is there anything unusual or important to know about Hood or the Cascades in December? My understanding is that rockfall is less likely but storms have a greater chance of mucking things up.
Watch the weather, it will come from the South so you should see it coming. If the weather is starting to get bad, go home. Do not climb into a storm. Taking compass bearings or using a GPS to get yourself back down in a white out is a good idea.