Thanks for getting back so quickly!
I'm evaluating frameworks and I have found Epub.js and Readium. Readium looks quite robust, but also quite hard to tame, Epub seems a bit easier to get familiar with. Also, I quite like the annotation related features as that's something I'm planning on doing too.
Ok I'll use the Gitter chat as you suggested. I think I will take a look at Epub.js first, trying to make the examples work, etc.
Thanks,
Janos