1. If your program is 1 year program and is clear printed on the documents such as your graduation letter and transcripts, IRCC will give you 1 year PGWP. But it depends on the officer'd decision, the officer might give you a shorter PGWP
2. If you applied PWGP online before your study permit expires, not sure which date your PGWP will be valid. It will be shown on your new PGWP and because your 1 year program it should be 1 year PGWP
3. If you apply your PGWP at border, the PGWP will be valid on the same date you get it and your study will be invalid. Also, it should be 1 year long PGWP, but might be shorter all depends on the decision of the officer.