with regard to the vest -- I am thinking that yes, if you switch companies the payments will stop and you will have to get approval with the new company and hopefully they will pay it off for you.
If there are no major problems with your current company I would stay with them and let the continue to pay for the vest. As far as plans goes, the copays that you have mentioned sound excellent -- there are a lot of folks out there paying co-insurance on top of copays or a straight percentage of appointments and medications, which needless to say would run anyone with CF into the poor house in about a week.
If you want to know for sure what would happen to your vest payments, check with the vest company and the insurance company -- there shouldn't be any reason why they wouldn't tell you what to expect. But my guess would be the safest thing is to stick with them till next year.