Hokkaido Golden Week Itinerary

We are going to Japan for 10 days in April/May (actually during Golden Week), and are focusing on Hokkaido this trip as that's the last major island we haven't been to yet. We have a general itinerary planned, but are a little unsure on the exact number of nights to stay at each location, or if we are completely missing something, so I'd appreciate any guidance or assistance.

Flight lands at NRT around 6PM, taking the NEX to Tokyo Station and going to spend the night/recuperate at the Hotel Metropolitan Tokyo Marunouchi.

Taking the Hayabusa Shinkansen to Hakodate, spending two nights in Hakodate (main focus the morning market, Mt. Hakodate, Goryokaku, the Botanic Gardens, and Tachimachi Cape. Primarily considering staying at JR Inn, Villa Concordia, or La Jolie Motomachi.

Renting a car from Hakodate and going to Onsen towns. Currently thinking of stopping by Lake Onuma on the route, then doing 1 night Toyako, 2 nights Noboribetsu, and 1 night Jozankei, but not really sure if we want to spend 4 nights in the various onsen towns. Primarily considering Lake View Toya Nonokaze or Toya Sun Palace for Toyako, Dai-Ichi Takimotokan or Noboribetsu Grand Hotel in Noboribetsu, and Shogetsu Grand, Jozankei Dai-ichi Suizantei, or Nukumorino-Yado Furukawa in Jozankei.

If we do the full 4 nights in the onsen towns, that leaves 3 nights in Sapporo, with at least a day trip planned for Otaru. Primarily considering 41Pieces, Solaria Nishitetsu, Onsen Ryokan Yuen Sapporo, Karaksa, or Cross Hotel in Sapporo.

Will fly back to Tokyo from Sapporo on our last morning, return flight leaves around 6PM and there's a JetStar domestic flight to NRT at 10AM.

I think my main questions would be, should we go anywhere else (considered going further north to Asahikawa), should we increase/decrease our time in any of our current locations, or any hotel recommendations (out of our primary list, or other options). Also, having never travelled during Golden Week, anything I need to be aware of? Already planning on getting the Shinkansen ticket a month out when reservations open up (and am seriously considering springing for GranClass)

Regarding the Shinkansen tickets. Just to put it into perspective. Year end is an other very busy travel time. So much so that JR gfreaked outh this year and has all seats on Nozomi trains on the Tokaidi reserved only from 28/Dec to I think 4/Jan. Well, I did fühlt but my ticket a month ahead of time for 28/Dec late afternoon. Including oversized luggage.
But I arrived very early at Tokyo station. So just before entering through the Shinkansen gates I changed my ticket to a train 30 min earlier. Done in under a minute in the app and got my new seat with oversized luggage and all.
A lot of fear mongering out there around GW and other high travel times.
So yes, get your ticket in advance but no need to be overly concerned.

Your schedule is fine. I like the idea of different Onsens so that you have variety. There is nothing like a Hokkaido Onsen experience

Since it's Golden Week, have you considered going to see the cherry blossoms, such s at Matsumae?

Yes, we are definitely planning some hanami time, although we had ruled out Matsumae since it was so far back south; not really convenient to reach via public transit, and if we did it after getting the rental car in Hakodate it would be close to 6 hours of driving to go to Matsumae then up to Toyako, as opposed to just 2 hours straight to Toyako. It looked like there was some good sakura viewing opportunities at Goryokaku and Hakodate Park in Hakodate, Temiya Park in Otaru, and Maruyama Park and Odori Park in Sapporo, and it looked like there were a few other strong contenders in and around Sapporo. I also figured there was a decent chance at there being some cherry blossoms around Lake Onuma, Lake Toya, and Lake Kuttara.