I'll answer a few.

1.) Compression ratio is how much the air/fuel mixture is compressed by the piston. So an engine with a 9:1 ratio would compress the mixture 9 times what is was before entering the cylinder.

2.) Offset is the distance between the centerline of the wheel and the mounting surface.

3.) Stock pistons are aluminum too. But aftermarket pistons that are forged will be stronger.

6.) I think it's to get the squeezing pressure more even acroos the pads.

7.) Yes, it will slightly reduce the grip of the rear tires when turning.