1) do I need to stay in Canada (after initial landing) to get the PR card?
I saw some conflicting info on the CIC site, one part says the card will be
mailed to your Canada address, another part says the card has to be picked up
in person at the local CIC office. It will be tough for me to stay in Canada for
2 months waiting for the PR card especially if I don't find a job in that duration.
You don't have to stay. The card will be mailed to an address you give immigration, at least if they believe you will be there when it arrives. If you were to tell them that you plan to leave in a week, they might hold it until you are back to stay.
If you have a secure mailing address with friends or family in Canada, you could use that. Otherwise, I believe you can arrange an address with UPS that will forward your mail to where you are. You would notify immigration of the UPS address you have arranged and your PR card should arrive there and be forwarded to you without immigration knowing about it.
If this doesn't work out, you can get your PR card when you are back for good. If it is within 6 months of your landing, you just notify them of your address. If it is later, you have to apply for the PR card and pay $50. In that case you would have to pick it up. That is true for PR cards you apply for later like that if you didn't get the initial one as well as renewals.
As for 2 months being hard because you can't get a job, if you want to keep the PR, you would at some point have to stay for 2 years. 2 years would also be hard if you can't find a job. In any case, unless you have a job offer, you realize you must show proof of funds when you apply for your PR as well as when you land. These funds are supposed to help you survive for up to 6 months while you look for a job.
2) how is the 5-year period calculated for retaining PR status, is this from the
date of initial landing? For eg - if I land on Jan 1st 2012, stay in Canada for 1 week
and then leave, then I return on Jan 1st 2015 (after 3 years) and reside in Canada
for 2 continuous years, then does that satisfy the 2 years out of 5 years requirement?
730 days in your first 5 years as a PR as well as any rolling 5 year period after that. You are right, if you stay for a week, come back exactly 3 years later and stay until the anniversary of your landing, you have your 730 days and can apply to renew your PR card which would at that point most likely be expired. It is however not a good idea to leave it for exactly the days you need to meet the residency requirements. I am assuming you have family somewhere and if there is a family emergency, you might want to go there, right?