No the one year validity is one year from the day of your medical exam.
Once you get your PR visa you are still officially not a PR. You have to “land” in Canada which I’m sure you already know. When you land you are officially a PR so your visitors visa (Canadian I assume) will no longer be valid as your status has changed (that’s my guess, make sure confirm this). I don’t know if they stamp “Cancelled” on your existing visitors visa when you send the passport.
EDIT: My answer is based on my US experience where you cannot hold two different visas (two statuses) at once. I don’t know if it’s similar or different for Canada but I would bet it’s similar. Once you are PR you technically cannot be a visitor or any other Canadian visa type.