In SVN you can just “svn checkout” the same http url to the directory. But I agree on the benefits of git, I mostly use svn for my own stuff that is sometimes random enough that I don’t bother to create a separate git repo etc.
Probably not too difficult actually. You can initially leave out all the amx_* files (platform libraries) to save space, because some of it is not even relevant for the nano. After you get the boot and LCD drawing working, the rest is probably very straightforward.