So in theory I could run a node that starts at the block height when my channel was opened & saves from then on?
Discussion
Yes, but pruned nodes don't work that way unless there's some options I'm unaware of. (I'm actually unsure if you can pick a starting block height, for instance.) No matter what your number was for saving however many gigs worth of blocks, you would eventually hit that limit and prune out your old blocks to make space for new ones.
Interesting thank you