First of all, congratulations on your Passport Request!!!
I don't know about your particular case but here's my advice:
- Your Visa (you will use this to be able to travel to Canada) and Letter of Introduction (which is the document you will show the Visa Officer at the port of entry to request your Study Permit), will most probably be issued with your program's end date + 90 days of validity.
- If you defer your intake, as you said, you have to inform IRCC via webform if the new start day is 150 days or more than the original date.
- If you defer, you will show the Visa Officer at the Port of Entry the updated LOA from your DLI, and your Study Permit should be issued with the new program end date + 90 days of validity. If for some reason it's issued in line with your Visa validity, you can always apply for a Study Permit Extension afterwards.
- You don't know when you will receive your stamped passport back from IRCC, so it might be better to secure a place right away for the following intake.
Good luck!