Hokkaido eating trip

Dear all,
We are travelling with a couple in their 60s who loves to eat and shop but gets bored with similar nature landscapes. I need some advice for my itinerary. We will arrive on 8th May.
Day 1 :Tomakomai
Day 2:Noboribetsu
Day 3: Lake Toya
Day 4: Hakodate enroute see Onuma Quasi Park
Day 5: Hakodate Sightseeing and Cherry blossom in Hakodate
Day 6: Drive to Otaru and stay 2 nights to enjoy fresh seafood
Day 7: Otaru
Day 8: Ashaikawa enroute Biei and Furano - eat nice foods here
Day 9: Takinoue Park/ Kamiyubetsu Tulip Park
Day 10: Sounkyo gorge
Day 11: Ashaikawa to Sapporo, return rental car
Day 12: Sapporo
Day 13: Sapporo
My itinerary is flexible so I am asking are there more places I should go for good food?
Are there any more fish market that I can add to my itinerary?
Is my route effective? Originally wanted to drive from Hakodate to Biei but realised since I will return the car in Sapporo then I should drive to Otaru first and that helps to break the journey.
Should I increase one more day in Hakodate? Not sure if I should drive all the way south for Cherry blossom.
This itinerary is made for the other couple who loves to eat.
After they leave Hokkaido, we plan to rent a small car and drive to all the national parks in the Eastern Hokkaido as we like to hike.

Thank you so much!
Would appreciate advice from all!

Hi! I can only speak to a portion of the question. You have basically captured many places for seafood like Otaru, Sapporo, and Hakodate. Sapporo has two seafood markets (Nijo and Central Wholesale) and Hakodate has one (Morning Market). I would advise eating at Hakodate specifically because of the raw ika (squid) where it might not be as available in other cities. I also find sashimi in Hakodate a bit cheaper than Sapporo. For snow crab I think any of those cities will be good. Sapporo has a famous snow crab restaurant where you can sample a multi-course meal just on snow crab.

In terms of Hakodate you might want to stay 1.5 days if possible. I assume the blossoms are at Goryokaku, so that is probably a few hours. The Red Brick Warehouses are cute and tranquil. I would highly recommend you visit Mt. Hakodate at night as the view is incredible.

Please check my user reports for Hakodate, Lake Toya, and Otaru as I went to Hokkaido in October 2017. I also went to Noboribetsu so let me know if you need more info. You can message me.

Dear Villagemayor
Thank you for your reply and information!
I am happy to know that I cover all the seafood market and I will eat to my heart's content in Hakodate since it is cheaper.
Can I also ask you about car rental versus Public transport?
It seems is quite easy to get around Chistose airport to Noribetsu, Lake Toya and Hakodate by JR train and bus so I was thinking I should skip the car rental as it seems the renting a car with insurance and using the highway will cost at least 8000 yen per day since we have to rent a ETC or pay HEP.
Of course, having a car is very convenient but if I do not fully maximise the usage since I will be doing a lot of walks in Noribetsu, Lake Toya and staying around in Hakodate so a 4 day flexible Hokkaido pass may be cheaper. There are only 2 of us.
Thanks again!

I think it totally depends on the season.