cocking the camera an lens
Yes when you cock the camera with the lens on, it cocks both. When you remove the lens, it will stay cocked unless you push in the tiny silver pin at the top and advance the pins at the green and red dots. That is how you can fire the lens independant of the camera and the camera independant of the lens. Just be sure to recock the lens by advancing the 2 pins to the dots again till they lock in place and check the body too.
If you should lock the lens on, don't force anything, there is a way to unlock it, DON'T FORCE ANYTHING! It's a paper clip job through a hole in the front just under the leatherete, top right corner.
The mirror thing may sound silly but it's a common mistake of nubies who look inside this monster for the first time. They think it's a bit cocked to one side and try forcing it and it will crack like an egg shell. I have plenty of mirror if you need so don't fret it if you do break it.
The lens you are getting is a non-C but is a great piece of glass. If the shutter goes on it, I can do that repair, you won't need a new shutter as Mamiya will tell you they can do for just $400 adn your first born and maybe an arm and just a leg as down payment.
Congratulations, it's a wonderfull camera adn if you ever feel brave, try fixing it yourself, it's a beautiful machine to work on.