Most instances will stop allowing new accounts to be created when it reaches a certain size that gets difficult to manage (hardware and moderating-wise). They self-regulate that way, and instances that get out of control will just be defederated by the others.
ZFS Raid Expansion has been released days ago in OpenZFS 2.3.0 : https://www.cyberciti.biz/linux-news/zfs-raidz-expansion-finally-here-in-version-2-3-0/
It might help you with deciding how much storage you want
I don’t know if that’s what you meant, but you can block JavaScript per-site, block first or third-party scripts separately, etc
Storing so many videos has a financial and ecological cost. When you reach thousands of hours of videos, it’s time to ask yourself if it’s really useful to keep them all.