1 -
BMW Software update web page. I've also had a lot of CarPlay connectivity issues on start up. I have an early production MY 2017 car and wonder if it's due to software. You could consider updating your software here, it may help with connectivity. Are these already updated with Over the Air updates?
2. Cost - was CarPlay not originally installed on your car? I thought BMW did not charge their $80/year subscription
until MY 2019 - I don't have a subscription for my MY 2017.
3. For initial connectivity issues, turning off and on Wifi often helps (80%+), if it never connects, restarting the iPhone always works for me.