On one hand they say that their data is completely free, and you are welcome to use it to create your own tiles from it, and they have no problem in you using their tiles for whatever. On the other hand they say that bulk downloading is "strongly discouraged", even though they also point out that maintaining their servers (for delivery) isn't free, and depends on contributors and sponsorships.
So how come it wouldn't be in their interest to let me download all the tiles, and then host them on my own domain? Also, just ball-parking it, how big would that be anyway, if i were to go up to
11 zoom, which seems sufficient for my interest.
Relevant document: https://operations.osmfoundation.org/policies/tiles/