Sounds good, Pie.
I notice you say "Can make whole book Bold to increase contrast". Do you find that specifying "bold" actually makes any difference? I use "Book Designer" to create my books and, in that, although "Bold" shows up fine in BD itself, it has absolutely no visual effect whatsoever on the Reader!
Does your tool support hyperlinks within a document? Those are very useful for things like footnotes, multiple-level TOCs in "anthologies", and so on.