Regarding using git-lfs for documentation:
I’ve done some tests - see details here: Should we use Git LFS to manage data?
In summary: git-lfs is not fully supported by GitHub web interface (for example, cannot upload git-lfs file trough web interface) and still not very robust (may break due to user errors, symlinks, merges, changing of git attributes, etc.).
Short term: I think we should not start using git-lfs now. Instead, we can store large documentation files (mainly screenshot files) as regular files. If we keep image sizes small then the repository size will remain manageable.
Long term: If we find that repository has become too large (not very likely to happen within a couple of years) then we can decide to move existing files to git-lfs or other solution that will be a state-of-the-art then. There is already a git-lfs command that can convert existing files to git-lfs files, so we could easily migrate any time we decide to do so.