1) For paraffin sections, you cannot overfix in formalin. In fact, for a mouse brain you could fix for one week at room temp to insure thorough fixation. With rabbit, I recommend 2 weeks minimum and even longer for larger species.
2) Yes, high paraffin temps can damage tissue. However, I'm not familiar with what the histokinet is. Is it a processor? If so, the temp for the paraffin should not be any higher than 60C on any equipment.
3) Yes, over dehydration is possible, especially with rodent tissue, which is leaner than human.
4) Store fixed tissue in 70% EtOH. Tissue can be stored this way for months, even years.
With all that said, I think the wrinkling you see on the slide is very typical for brain tissue. Try increasing the waterbath temp and let the sections float for a while and spread out. Avoid cutting blocks that are too cold. Brain cuts best at almost room temp.
I hope all this helps and good luck.