TGIT should allow cloning and/or creating from within a non-empty repository
TGIT has no GUI interface for cloning a repository or creating a repository from with a non-empty folder of a git repository. It should have, since this operation is perfectly legal using git itself. TGIT does allow cloning or creating a repository from within an empty folder of a git repository through the Shift-ContextMenu interface. But there is absolutely no reason to distinguish between an empty or a non-empty repository in this case since cloning or creating a repository within an already existing repository folder does not affect any of the repository files already in that folder.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information