1. It's not unusual to be stiff at first, but shouldn't be too hard to turn. I have cut 6 layers with mine that have a fusible on them without any problems at all.
2. & 4. The mats do get cuts in them, but they will continue to work for quite a while. Use opposite ends/sides and that will help make them last longer. When you start getting a lot of places that don't cut, it's time to replace the mat. As for using the Olfa mat, I wouldn't. Accuquilt has made their mats for their specs and a mat that is a bit harder or thicker could very well damage the blades or even break the roller. The mats aren't that expensive and I keep several of each size on hand.
3. You should remove all the pieces stuck by the blade if possible. A soft brush can also be used, just don't use anything that will damage the foam around the blade.
I hope this helps! I definitely recommend joining the Accuquilt group on yahoo as it is very informative.