Yes, you can have up to five vehicles active on the auto-pay membership at one time. You may have up to ten vehicles listed on your account at once (5 being active and 5 not active on the auto-pay membership.)
If you see the message "You've reached the maximum vehicle limit of 10" in myQQ it is because you have 10 vehicles associated with your account.
myQQ has a imposed limit of 10 cars. We do this to help ensure that you are able to quickly access the cars on your account, and to make sure the experience is quick and stable for managing this number of cars.
If you have exceeded your vehicle limit and need to remove vehicles that you do not want associated with your account, please follow the directions to remove vehicles with myQQ or visit a store.
This does not apply to active cars on a membership. The limit for active cars is (also known as "Flock") is 5 cars.