Also, would kind of had preferred to read "I've not used GNU Radio much before, but I've played around with the LiveDVD (or whatever you'd have done)" instead of reading "I've not used GNU Radio before(at all)" and seeing you use pretty dated screenshots from Josh's website instead of familiarizing yourself quickly, so that you could leave us with the certainty that hey, we don't have to teach you how to even start GRC ... not that I really think this will be any trouble for you, but the ease of getting started with GNU Radio, considering ready-made packages and the bootable liveDVD and the guided tutorials make me wonder much more why you didn't demonstrate you've played with GNU Radio before.
Big Plus is of course that you mention Cheetah, which proves you've actually looked at the source code, I guess! This is probably not going to hurt at this stage, but as Ben said, we're currently replacing that with Mako (Cheetah is kinda Python2 only, and we're making things work with Py3).
So, I hope this is not asking too much from your time right now (you might be busy with exams for all I know about studying), but I'd recommend you checkout the "next" branch of the gnuradio repository, and try to build it with GRC enabled, and maybe add some "change <filename/directory> to include <functionality>" to your timeline after getting a rough idea of how code gen works there.
I like your block diagram, it clarifies a few things, and generally, I prefer reading a concise chart instead of a wall of text, and I think that "writing down" the current code generation process in terms of who-calls-what in Python in that shape would be awesome, because that would allow you to make a second, modified chart that shows what you'd like to add/change to that, and would also be a great starting point for the (relatively compact) documentation we'd like you to deliver in the end.