Here is a list of autumn foliage destinations in Hokkaido in mid-October. Asterisks indicate multiple entries at the curation sites I looked into. Jozankei has 8 entries, Sapporo 6, Sounkyo 5, Noboribetsu 5, Akan 5, Shikotsu 4, and Shiretoko 4. Unless you want to do an adventure, drop destinations far from Chitose, such as Shiretoko and Akan. Sounkyo and Onuma are still far, but including one would be borderline. Jozankei, Sapporo, Noboribetsu, and Shikotsu would be a core. Try to include less known sites with no asterisk.
* Shiretoko Five Lakes
* Shiretoko Pass
Akan Lake Onneto
* Lake Akan
* Lake Kussharo
Nayoro Nabo Tunnel
Shumarinai Nature Park
Takinoue Keikoku Kinsenkyo Gorge
***** Sounkyo Obako
Ginga & Ryusei no Taki Waterfalls
Asahikawa Kamui Kotan
Mikasa Katsurazawa Koen Park
Sunagawa Hokkaido Kodomo no Kuni, Kids World
* Hidaka Iwanai Senkyo Gorge
Goshiki Keikoku Gorge
Sarugawa Keikoku Gorge
Shimukappu Akaiwa Seigan Kyo Gorge
** Takinoue Koen Park
* Sapporo Maruyama Park
* Eniwa Keikoku Gorge
* Takino Suzuran Hillside Park
* Mt Moiwa Ropeway
* Nishioka Park
Monami Park
Nakajima Koen Park
******* Jozankei Jozankei Dam
Hoheikyo Dam
Chitose Aoba Park
*** Lake Shikotsu
***** Noboribetsu Jigokudani Hell Valley
Orofure Pass
Shin Noboribetsu Ohashi Bridge
* Lake Toya
Kyogoku Fukidashi Koen Park
Niseko Iwaonupuri
Kagaminuma Pond
Kuromatsunai Garo Kogen Highland
Yakumo Unsekikyo Gorge
** Onuma Quasi National Park
Here is one of the conservative routes, including neither Sounkyo nor Onuma.
Chitose
Noboribetsu (1)
Lake Toya (1), needs car hereafter
Lake Shikotsu (1)
Eniwa
Suzuran
Jozankei (1)
Otaru (1), no more car hereafter
Sapporo (3)
Rera Mall
Chitose
https://www.env.go.jp/en/nature/nps/park/shikotsu/index.htmlhttps://www.env.go.jp/park/common/data/06_shikotsu_map_e.pdfAn adventure version.
Chitose
The overnight bus from Sapporo to Shiretoko (2), check in a car there
Akan (1)
Lake Onneto
Mikuni Pass
Sounkyo (1)
Tokachidake Bogakudai Observatory
Furano (1)
Mitsui Mall
Sapporo (3), check out the car on arrival
Chitose
https://www.env.go.jp/en/nature/nps/park/shiretoko/index.htmlhttps://www.env.go.jp/park/common/data/02_shiretoko_map_e.pdfhttps://www.env.go.jp/en/nature/nps/park/akan/index.htmlhttps://www.env.go.jp/park/common/data/03_akan_map_e.pdfhttps://www.env.go.jp/en/nature/nps/park/daisetsu/index.htmlhttps://www.env.go.jp/park/common/data/05_daisetsu_map_e.pdf