To answer each question, you need to find the type of your vehicle (passenger or motor:(
1. Find the FMV of your vehicle in Sep 2019. You can use websites such as https://www.carfax.ca/car-valuation
If your car is worth $30,000 or less before tax, use the max threshold of $30,000 as your CCA class 10
However, if the FMV is less then use the actual estimated value,
If the FMV is more than $30,000 before tax, use the actual FMV in your CCA class 10.1
2. Use the half-year rule to claim the CCA
You will need to prorate the expenses based on the mileage you used:
for example;
If your business use in the three months was 20,000 km while the total use for business and personal is 40,000 km, multiply the expenses and the CCA by 20,000/40,000
make sure you use the same rate for expenses accrued in the three months (you cannot claim the expenses prior to the business use of the car).
3. Your vehicle (A) should be declared as a deemed disposition in Dec (which is the FMV in Dec). Since you have already claimed CCA for it, you will need to assume that you disposed it in Dec and report any difference in values between the FMV in Sep and the FMV in Dec as Capital Gain. And the difference in value between the FMV in Dec and the depreciable value as recapture
Keep in mind you don't have to claim the CCA on the vehicle (A) if it is not worth it. you can use the mileage rate to claim other expenses only.
Refer to the first link to check how to claim the lease amount.
I hope this was helpful
