The more difficult terrain is in the southern end where you're crossing over mountains. The northern half is flatter, passing by lots of lakes and ponds. You'll have to decide for yourself whether you'd prefer to tackle the tougher southern end right away so you can cruise through the end.... or whether you'd prefer to have an easier "warm up" by cruising through the northern half first. (This assumes you are not counting Katahdin in your 100-Mile Wilderness trek...)
When I hiked the 100-Mile Wilderness, I parked my car on Golden Road for a week without a problem.
For what it's worth, I headed north... didn't see very many people at all, though it was pouring rain most of the time. A friend was a day ahead of me and competing for space at the same shelters I had all to myself a day later. It's all about where you are in the bubble, I guess.
If you have multiple people and only want to take one car, I'd highly recommend what we did -- we parked on Golden Road and took a Katahdin Air float plane ride to Spectacle Pond. It was few years ago so maybe things have changed... but it cost only a few dollars more per person than a shuttle ride from Golden Road to Monson. Since it rained most of the trip, the flight was one of the few places where I had any views so it was worth every penny.
Enjoy!
- Ivy