Answers to your questions, based on my application experience:
1. Yes, job offer is sufficient and it should be on Company Letter head. It should have, You Name, Designation, Roles & Responsibilities, Hours per week (like 40 Hours or something), your Salary.
2. In my case, my company is at many places in Canada but they have one office in Alberta. I used that address as my work location.
3. Getting NOI, it is not always couple of days. But maximum I have heard is 14 days. You will get this NOI in the email (keep checking spams as well), that email will have a link (with expiry of 30 days) for you to create account on Alberta PNP portal. You have to fill the complete details (much like EE profile creation). Attach all the required docs and submit your application (along with a fee of CAD 500). Once you submit this, Alberta PNP will take their own time (it is not fixed how many days they will take to make a decision to nominate you, In my case they took 4 working days) to approve or decline you a nomination.
4. Once you get the nomination, you will get 2 emails from Alberta PNP (one with password protected PNP pdf and other will have the password to open this pdf).
5. You will get another email from IRCC, to login and accept the PNP from Alberta. Once you login, be very careful in accepting the nomination (as the decline button is very near to that).
6. Once you accept that, you will get 600 points and most likely you will get the ITA from IRCC in the next draw (General or PNP).