Apparently I am famous now
If you need any help just send me PM.

To answer some of your questions:
Distribution - Package as deb file that installs the files into /usr/share/themes and then the theme will be picked up in the theme settings app (Can also be manually done with a zip file)

Breaking - I am fluent with CSS, but from what I have seen in harmattan css in some cases identifiers dont work, so if you end up putting one in that isnt supported, yes you can break the device easily. Keep flasher open and just use R&D and SSH to patch to a stable theme. (I have a few themes installed that I can always fall back on.)

Hope that helps you