I like your idea regarding worshipping a portfolio. It does indeed let us introduce credible ancestor/totem worship without messing with the gods list (which I am solidly opposed to doing). We would merely have to explain why a CE tribe could warship portfolios of Protection and War, which are domains of Adenan. For example.
I dislike the idea of saying all dead reside in Underworld. It's always been sort of a clearing house for the gods to come get their faithful, which is an important part of the religion. I don't think it'll kill anything to make that change, but we'd have to explain just *why* a person would bother worshipping a god if, in the end, none of it mattered in the everlasting afterlife.
I am utterly unconcerned with overlapping portfolios, since two gods with a shared portfolio would simply be relevant to different aspects of that portfolio. I don't think there's a lot of shared portfolios anyway, though, due to the method we used to create the gods, but I could be wrong. Again, not a concern of mine though.