First, I think you should store your tobacco, however packaged, in a stable consistent humidity and temperature environment. If possible. I have smoked with a few SG FVF and BBF that were 8 to 10 years old without any problems. I think sealing each tin in its own Mylar bag is like wearing suspenders with a belt. Expensive, time consuming and takes up much more space.
If you’re really that concerned, separate out your tins you plan to age 10 years plus. Buy some thick 5 gallon Mylar bags and store many tins in the large bags.
The other thing to consider is the % of waste is going to be quite low if you do nothing. I believe less than 5%. But 5% more than you think you’ll need and live with the losses. I recently opened a ton of Wessex something or other that has the seal broken. The tobacco was very dry but not crumble to dust dry. The tin was fabulous. Moral of story? People spend way too much time worrying about this issue.