Hi Marcin,
First: welcome to the beam community! And great that you would like to work on a Zotonic project.
Michael answered already most of your questions, I think.
The ideas are indeed just that, ideas. Things that we came up with while brainstorming.
I personally think that idea 6 (OTP-ification) might be a bit big, as it is almost a “everything or nothing” project..
Idea 5 (the stats) is something you can make as large or small as you like, so that will fit one summer-of-code.
Last year we worked together using Google Docs for editing the proposals, that way it was easy to comment and share between you, the mentors and the zotonic developers.
Looking forward to see your ideas!
Marc Worrell