1) No. The only risk from your beer sitting on a yeast cake for extended lengths of time is autolysis, and that's not even a concern unless your primary is longer than two months.
2) It shouldn't cause any problems with the fermentation, but I think you'd get more hop/oak flavor if you waited until after fermentation was complete. I've been told that oaking works best if you do rack to secondary, but I haven't tried it myself. I've only oaked one batch, and I did it in primary. Came out tasty as all get out.