Mamiya 645 Super - newbie help please!

I am playing with a loaned Mamiya 645 Super. Would someone please help me a little with things I cannot find in the manual? I have found the manual for the camera itself, but not for the grip or the finder.

1) What is the "START" position on the power grip for?

2) On AE prism finder, I see AV, Auto-AS, and SP position. What are these?

3) With standard 80mm N lens attached and looking into a view finder, and into a bright light, I see a faint diagonal line on right side of the view finder crossing the vertical portion of square right in the middle. Looks like an internal reflection to me. On left side I see the same thing but it is VERY faint - almost invisible. I cannot see it with 150mm lens. It also does not rotate when I partially un-mount the lens and rotate. Is anyone familiar with this?

One more...

Can I lock the auto exposure? In other words, can I point at something, let AE measure and determine the correct exposure, LOCK IT THERE to recompose? Similar to what half-button shutter do with most of 35mm SLR?

Yet, one more...

When a roll of film is finished, manual says to wind the crank until free. I can't do that with power winder attached. Is this going to happen automatically or do I need to do something else?

This is my understanding:
(1) After loading the film,set the white dot to "start",the film is automatically advanced to the first frame.
Also if attaching a loaded holder in mid-roll do this.
(2) AV is average metering
AUTO A-S the camera automatically selects AV or Spot according to the lighting situation
SP is spot metering,use the circle in the center of the focussing screen as a guide.
For AE photography the shutter speed dial should be set to the red dot, or if you like the red square which allows the exposure to be locked before re-framing.The AM lever on the lens must be set to A.
(3)My Super with 80mm pointed at a room light,I don't see any lines.
(4)At the end of a film my power winder just keeps going till I turn the white dot to off.
I like this camera,some of my best shots were done with it.

Thank you.

I went around my house pointing lens at lights, and I can no longer see the lines. That could have been some strange reflection caused by a particular light fixture. I can't reproduce this now.

Alan's mostly got it covered as I understand things (I never can remember between the red square and dot), but I'll add a couple things.

After I've fired the last shot using my motor drive, the winder automatically winds the film to the end and then stops. This seems like logical behavior, so I can only guess that maybe Alan's is behaving a little off he's got the other model and it wasn't quite as refined.

A niggling little trait that took me some time to figure out is that if you finish off the film in one film back and then swap on another one that's already partially shot, the shutter on the body will not be cocked. Flipping the motor drive switch to "Start" will cock the shutter for you without advancing the film.