Another things is, i am not sure to which degree github can keep different versions of files. That would be most interesting especially for *.RMP, *.MAP, and MCD Tilesets. Does anyone know if there is a list of supported formats out there?
Git will always keep all versions of the files you put under control. Per commit it will save the complete files that were changed (compressed using zlib)
In the worst case (when your file cannot be compressed easily via zlib) it will store a full binary blob of the complete file.
Besides that, i wouldn't worry about it to much for mods. Most files are quite small, and it is unlikely a repository will meet 1GB in short to medium time. And even if it grows too large, you can always start a new cleaned up repository version by doing some git-fu.
I'm not saying I don't want anything to do with the project, I think I've already expressed my enthusiasm enough. But I'm not prepared to learn it all right now.
As for learning git ... if you are not interested in doing fancy things you might just as well get away with using a good gui that lets you perform the following tasks easily:
* add/remove files
* Display differences between current work and last commit
* Let you store those differences as a new commit (preferably by requiring some sort of commit message with a summary of those changes)
* Let you push/pull to/from the github version.
For more advanced things like merging and solving commits you can always ask the community, so no need to worry about that at the moment.