I have a question concerning the 30gb promotion when you buy a new phone. Is it 30gb extra that you can use every month meaning I could take 0 gb for the first months (until I run out) or do they expire.
If you check the legal notes at the bottom of the page, it is pretty clear:
Offer valid until December 13, 2021, inclusively, with the purchase of a new or Preloved phone on fizz.ca. Expect on average a 30-day delay following the receipt of your phone to see this My Rewards perk of 30 GB deposited in your account. Once deposited, this perk will be available for activation for 60 days, and once activated on your mobile plan you’ll have 60 days to use it after which this My Rewards perk of 30 GB will expire. My Rewards perk are not redeemable for cash and cannot be transferred. The terms and conditions of the My Rewards program apply.
Hope it is clear.
Like Emporium said, it is under certain conditions.
Also what is cool with Fizz is that you can change your plan every month. Once you can actually activate those 30GB then you could also reduce your plan to save some money temporarily until they run out. Then you get back to a plan you like. Make sure you don't abandon a grandfathered rate while doing so...
So to follow your logic, you can do like your suggested use case but after the said delay. Make sure that you understand if you run out completely and have a 0GB plan, nobody can gift you data. You must pay at least 1GB to receive data (except for perks).