1. Yes, epubs and kepubs have different font sizes, unless you apply a patch that fixes it
2. Right, no stats with epubs
3. Yes, settings are saved for each book
4. Also true. To change this with a book sideloaded from Calibre, change the <p> tags to <br> tags in the comments section (the html view). Unfortunately it must be done manually with each book, as the bulk option won't stick