4 days seems a little rush for this itin. As such you shld take the Expressway to save time. From Hako to Otaru, half of journey does not have Eway.
Whether HEP is worth or not kind of depends where u r returning your car ...
A) if u r returning car at Otaru ... and
if the leg from Chitose to Hakodate falls on a weekend/public holiday, you can just rent a ETC card which gives u 30% discount on tolls
... this is the longest Eway leg and most costly. if can get 30% just on this leg, ETC shld be enuf and cost less than HEP
B) if u r returning your car at Chitose, then I think just get HEP bcos Otaru to Chitose is also quite far and costly via Expressway... and it's not on a weekend
HEP goes by calendar days matching your car period rental. Yours will be the 4D package
Re Insurance, besides Vehicle Damage Excess (CDW) 50k and NOC 20k/50k, there is also excess on Property Damage of 50k.
Your personal travel insurance may have cover for Rental Vehicle Excess to cover CDW and perhaps Personal Liability to cover Property Damage, but from policy wordings NOC may not be covered by Travel Insurance.
if u r in a group of 3-4, might as well get the full insurance which shld not cost much for just 4 days (maybe JPY 2-3k more per day) and for peace of mind.
use this to check the tolls http://dc.c-nexco.co.jp/dc/DriveCom...65&e_ic_cd=001&optCrTp=2&optSrt=time&ca=hokka