When is your existing passport going to expire? You can submit the application using your existing passport and then send a CSE with new passport details.
I had submitted my Application and medical with my old passport and after new passport, have requested them to update my passport number on application. Called CIC agent, he said its in Ottawa office and asked to contact them. I send email to CPC Ottawa and attached new and old passport (scanned).
You can have your medical on your current passport and later update them with new passport number.
Yes and when you get your passport back, send email to CPC Ottawa. They will update information and send you update acknowledgment email in a day or two way faster than CSE. I got my acknowledgement email 2nd day (today).
Your medicals are valid for one year. So during that time if you renew your passport it won't affect the validity of your medicals. Update CIC when you renew your passport.