Work flow for publishing figures under Common Creative license (in order to ease re-use in journal publications)
The software used to create a work does not change anything with respect to the its copyright status.  I can create a work in Photoshop and distribute it (the work) under CC-0 if I want.  The fact that someone needs to have a non-free software to open it isn't important. Where things could get tricky for something like a PS file is if each layer has elements that could be considered fair use within the overall final image may be being distributed in full and hence no longer subject to fair use exceptions.  That won't be concern for most LᴬTEX / TikZ stuff

You seem to be talking only about the final version of figures, so CC-BY should be fine.  If you want to release the LᴬTEX / TikZ code, it seems that Creative Commons is indeed the preferred license type in the community (see TeXample.net which requires user to submit their TikZ stuff as CC-licensed works).  If the code is GPLv2, though, the visual result isn't covered by GPLv2.

The correct attribution will depend on your style guide.  I don't think you would go wrong to follow whatever standard it uses for works of art unless there is a more specific format in your style guide.

I'm not aware of any workflows to do this, but they shouldn't be too hard to write if you're using that many figures that it's worth your time.