The only SVN repository we are using now is the ImpressCMS SourceForge Project's SVN Repository.
The URL to enter in TortoiseSVN is : https://impresscms.svn.sourceforge.net/svnroot/impresscms/
You can browse SVN here
I propose we use the Trunk to hold latest stable code. We develop everything in branches or tasks and every time a feature has been tested and revised, it gets merged to the trunk. That way, our trunk always stays as much as possible workable. Early adopter users can use the trunk to test the latest edgy-but-tested stuff...
For now, I suggest we directly develop in the trunk until our first release.