Glad to hear that EPUB will be worked in somewhere. I'm not familiar with Lemon8, so wasn't sure how/if that would help matters.
Our "best" practices guide quickly turned into a "better" practices guide when we realized what a dog's breakfast exporting can be: one of the main stumbling blocks was the absence of a clean export option from desktop publishing programs like InDesign, which is what most publishers are using for design/layout. We ended up outlining three alternative workflows (editing/applying styles in InDesign, Dreamweaver, or Sigil), all of which end with an open source tool like Calibre or Sigil. In our guide, we also provide a general introduction to the EPUB format, its features and limitations, and some considerations about ebook design, validation, distribution, etc. The guide will be available for free as an EPUB or through our wiki in the near future: I'll make sure to post the link here!
I have been speaking with scholarly presses about their electronic publishing practices, and it appears that everyone is outsourcing EPUB production. I really hope that OMP will offer an efficient, affordable alternative so that these conversions can be performed in house and with minimal fuss.