You fail to answer even one of the questions, why because to answer honestly and specifically would damage your ideology?
"...costs and coverage changes will occur" currently Medicare is 80/20 so any coverage that is not 80/20 would change. This change would seem a boon to Medicaid recipients but not so favorable to current VA recipients. https://www.quora.com/If-a-single-payer-health-care-system-was-put-in-place-what-would-happen-to-the-people-who-work-in-the-insurance-industry

Many of those moved from private plans to Medicare-for-all would require a Medigap/Medicare Advantage-type plan to continue similar coverage. 

"To help cover Medicare’s cost-sharing requirements, most people on Medicare have some source of coverage that supplements Medicare, including Medigap policies (23%), employer or union-sponsored retiree health plans (35%), and Medicaid for individuals with low-incomes (19%)." http://www.kff.org/medicare/issue-brief/medigap-enrollment-among-new-medicare-beneficiaries/