4 day relaxing trip to Hokkaido in early June

I'm planning a rather short trip to Hokkaido from June 1 - June 4 to celebrate our 10 year wedding anniversary. We love Japanese food, being in nature, and exploring...we are from HK so we don't need to see city life, however, we do enjoy very much wondering through quiet streets in Japan.

After doing some research I'm slowly realizing that 4 days is really short to truly experience Hokkaido ...but given that we do have limited time, we don't plan to be too ambitious... We plan to rent a car if it can make traveling around easier. I don't have an itinerary yet but have some questions.

- We will be arriving at and departing from the New Chitose Airport.
- Otaru seems like a highly recommended spot - would it make sense to set our base there and take short day trips? or is this a truly day trip destination?
- I would love to see some flowers but it seems that early June is too early for Lavenders in Furano but tulip in Kamiyubetsu seems to be too far to travel for such a short trip. Any other potential good flower places to visit in early June?
- I know there are some really awesome lakes...Lake Toya and Lake Akan look beautiful. What would be a good one to visit given our short visit?
- Is Sapporo worth the visit? Or is the time better spent in Noboribetsu (the Demon's fire trail sounds pretty awesome)
- Given our tight schedule, should we set our base somewhere or move around? And if we move around, I'm not quiet sure whether we should go west or east...

It would be great to get suggestions for some easy and relaxing traveling for 4 days...and also any good recommendation for accommodation would be greatly appreciated to help make this a special anniversary.

Otaru is more of a half day trip from Sapporo than anything else.

Given the time restrictions I would go to Lake Toya. Combine that with an overnight stay at Noboribetsu Onsen.

As for the flowers, there are fields of other flowers at Furano in early June
http://www.farm-tomita.co.jp/en/farm/flower_guide.asp?id=5
http://www.farm-tomita.co.jp/en/farm/flower_guide.asp?id=6
http://www.farm-tomita.co.jp/en/farm/flower_guide.asp?id=1
http://www.farm-tomita.co.jp/en/farm/flower_guide.asp?id=10
and the Greenhouse http://www.farm-tomita.co.jp/en/farm/flower_guide.asp?id=9
The lavender soft serve ice cream is available too. Yum.

You can easily travel by train between the airport, Sapporo, Otaru, Lake Toya (bus or taxi from the train station) and Noboribetsu (bus from there to Noboribetsu Onsen). For Furano a hire car is a lot easier.

If it were my anniversary I'd do something like this:
1 June: arrive New Chitose Airport, catch the train to Toyako Station (Lake Toya), then in the afternoon head to Noboribetsu Onsen via train and bus. Overnight Noboribetsu Onsen
2 June: walk the trails around the jigokudani, then late morning to Otaru by train for the afternoon. Head to Sapporo in the late afternoon/evening. Dinner there (ramen alley perhaps?) and overnight somewhere centrally located.
3 June: Pick up a hire car by about 8am, drive to Furano. In the early afternoon drive to Asahidake Onsen. Overnight there. Go up the ropeway to Asahidake if you have, or visit in the morning.
4 June: More onsen and exploration. Head to the airport.

Also, if it were me I'd stay here http://www.takimotokan.co.jp/english/ (I wished I had stayed there!!!)
We stayed here http://travel.rakuten.com/hotel/Japan-Hokkaido-Higashikawa-Asahidake_O... It was probably "Grand" several decades ago but despite being rundown the food was very good and the Japanese style room was also good.
These other ones look less rustic however they have western beds
http://travel.rakuten.com/hotel/Japan-Hokkaido-Higashikawa-La_Vista_Da...
http://travel.rakuten.com/hotel/Japan-Hokkaido-Higashikawa-Asahidake_M...
http://travel.rakuten.com/hotel/Japan-Hokkaido-Higashikawa-Asahidake_M...

you are young-have dinner at sapporo beer garden-not sure if you are at sapporo during great food festival at hokkaido university-i hiked in mountains of sapporo last year so instead of doing a lot of traveling around, just do a little-go to otaru for 1/2 day-i always enjoy noborbetsu

Thank you all for your recommendations. I'm going to revise some of our plans to make it more relaxing :-)