FYI, I'm not exactly an expert at creating ePub files from scratch - I'm too lazy
I let Calibre do most of the hard work for me, and just tweaked the resulting ePub to improve performance.
If Sigil had been around when I created my version of the Bible, I probably would have given that a go - alas Sigil was probably just a little something in the back of Valloric's mind at the time.