Gosh no, you don't need new prints!!!!! The prints you already have are fine.
This will be a problem. Millers and Mpix are shit.
For the actual act of calibration, you should be in as dim light as possible. So yes, definitely close the blinds for that.
For the actual editing, bright light is good, as long as it's not hitting you directly.
Maybe you could show me a photo of your room?