Hi JanKhai
I'm now living in Hokkaido.
As indicated above, late October is a bit later (not too later) than the best timing to see autumn leaves. Anyway, if you want to watch autumn colors, visit major autumn color spots soon, because the first snowfall will soon come only within one or two weeks after you depart from Hokkaido.
In Sapporo you will usually see the first snowfall around the second week of November, while in colder highland places like Daisetuzan (Mt. Daisetsu) you can see autumn leaves even in mid-September.
Moving around rural Hokkaido by a rented car is far easier than driving in crowded cities like Tokyo or Osaka, because most major roads in Hokkaido are well-maintained and straight. You will seldom see dirt roads unless you move deeply into unknown mountains or within a farm. Take a look at this YouTube video:
http://www.youtube.com/watch?v=-3gvGYgV4yoThis is a road typically seen in countryside Hokkaido.
Please remember that you will find only a few gas stations and convenience stores depending on your driving areas. When you are moving around very rural Hokkaido near Russia, you will see most gas stations are already closed at 6:00 pm. There is a well-known area near Wakkanai city where you can't find any gas station even by driving over a distance of 80 km. So, if you're unsure about whether you can find next gas station or not, visit a nearby gas station you can see then. I have often heard on local TV programs that people driving around Wakkanai by a rented car give up driving and call for emergency help due to out of gas.
If you use public transportation, check carefully its timetable. It's very important for all tourists visiting rural Hokkaido to see exactly when a bus or train will come. If you fail to catch it, you may wait for two or three hours at a bus stop or train station, or have to find a nearby inn.
By the way, New-Chitose Airport is located in Chitose city, not in Sapporo. This airport is about 40 km south of Sapporo. It takes about one hour by car to reach central Sapporo.
Typical autumn color spots near the Chitose airport are:
Jozankei and Nakayama Pass (in a south-west district of Sapporo)
Eniwa River and Eniwa Gorge
and
Lake Shikotsu
Here are two YouTube videos showing how the Eniwa gorge look like in mid-October:
http://www.youtube.com/watch?v=2z_vDznnKcghttp://www.youtube.com/watch?v=AWqOB_memsc