To answer your questions:
- No, you can renew your PR Card as many times as you like, provided you meet the requirements. There is no obligation to become a citizen, or to leave after a certain number of years. There are people who have lived in Canada for decades and not yet become citizens.
- If you submitted acceptable proof of urgency, the goal is to get you your PR Card before you have to travel. This is different for each case. We can reasonably assume that, once the applications have been opened, applicants who are travelling sooner are given greater priority, but this is just a guess. In our experience, urgent processing time normally averages out to around 20-30 business days. However, currently (January 2016), there is some kind of issue at the PR Card-issuing facility and there is no guarantee that you will get your card in time.