Publishing at a venue without ACM/IEEE brand?
Not being affiliated with an organization such as the IEEE or ACM is not, on its own, a bad sign. For example, what is currently the IEEE Conference on Computational Complexity has decided to end its affiliation with the IEEE and go solo; the Symposium on Computational Geometry likewise just left ACM. STACS is also unaffiliated.

It's not great if the proceedings are only distributed on CD. On the other hand, if you're already going to be preparing a journal version (and you should!), that will completely supersede any conference version, anyway. I would never read a conference version ("extended abstract") of a paper if a full version was available: in my area (theoretical CS), the conference version generally has the proofs missing and the peer review isn't very rigorous.

STACS publishes proceedings through Dagstuhl, which is basically a computer science conference centre in Germany and has close links to DBLP. In this case, copyright is retained by the authors. Note that, regardless of who owns the copyright, most CS conferences won't accept papers which have either appeared at another conference with published proceedings or have been submitted to such a conference. You don't get to double-dip your papers.