To be prepared for the Rapid Developer certification I just recommend to do all the paths of the beginner and the rapid level
The grey and green ones from the academy
With this you will be ready to do the exam that is completely online and there is no limit of time so you can do it at your own pace without problems. Also you can consult all the information you want during the exam
To answer your last questions I would use your company email don’t worry because if you left that company you can transfer all your data to a new account.
It’s called “merge accounts” it’s inside the configuration of your profile in the advanced tab.
If you have further questions let me know!,
Thanks for clearing my doubts.