e39, 2001 530i - rear brake caliper bracket

HI all

Just changing my rear brake disc and pads and I have a few questions:

1. The lower caliper bracket bolt is very inaccesible to torque to recommended setting - is it okay if I make it real tight and leave?
2. These caliper bolts don't appear to be a 16mm bolt! And I'm started to round the head, slightly, is it worth changing and can anyone tell me what exactly are the size of these caliper bracket bolts?
3. I noticed the rear discs to rub slightly against the handbrake shoes is this normal, again it is only a light friction sound?

Thanks for all your help.

Matt