I am going to Hakodate, Lake Toya, Noboribetsu, Furano, Biei, Asahidake, Sounkyo, Otaru, and Sapporo in 13 days. Everyone travel in different style, some are more energetic and can travel fast paced; as you can see, I am the very slow type (and I donft like to drive at night).
I donft know the Japanesefs view on walk-in guests, I only know if you book a place which includes dinner, they will expect you to arrive on time so they can prepare meals. I am hoping to book all accommodations before I go so I can look for places I like within my budget. If you are going at peak season/ weekends, choices might be limited if you walk-in.
For my traveling period, Nissan is still offering low season rate while Mazda is on high season so Nissan will be cheaper for me. It usually takes Tocoo a few days to reply so they might get back to you soon.
Here is a website that I found very helpful, you can work out the driving time and distance between places so you can get better idea on how much you can cover in a day.
Happy planning, this is my first time to Hokkaido and I am very excited about it :)