1) I can prepare and upload it here, but I think it more useful commit it to community/themes folder in repository. Is it free for commit or you yourself decide what to make of this branch of the repository?

1. Pls. get an sf.net account and send me the account name
2. Team members can commit translation and themes on their own in our dev repository, nevertheless I got most contributions as patch or plain file
3. Code changes on the core require a code review so the best way is to send / attach the patches or you point to a personal repository where the changes can pulled from. Accepted team members can push their patches to the dev repo on their own, but this does not replace the discussion about the issue in the first place. Additionally a common workflow for Mercurial must be established after the next release.

2) "but you asking where and how you can pull the lastest code changes /fixes?" yes, absolutely. Now I integrate 5.0rc and find some errors. Some errors I can fix myself, without needs to contribute it in bugtracker. So, what best behaviour in this situation?

1. send me the patches OR add an issue to the bugtracker and attach them there
2. create a personal repo on sf.net -> push your clone there -> add a branch [Squashed bugs or so] and send me a "Pull request"
3. Contribution Guide (draft)