No, you're not crazy. You're asking good questions and thinking about what you're doing.
This is one of the problems that one encounters when mixing pantheons. Although both Cernunnos and Danu are Celtic, remember that the Celts were not a single nation-state. They were a tribal people. Cernunnos was Gaulish while Danu came from Ireland. They are about as far different as Greek and Germanic in terms of being from a particular pantheon.
That being said, Danu's consort (Bile') (pronounsed bee lay was reputed to be the God of Death and also of Life. This is similar to the role filled by Cernunnos in Gaulish myths. So one could make a case for them being the same Deity if that made things easier for you.
How were you planning on re-enacting the Sacred Marriage when you are working as a Solitary?