Right - multipiece backs - I have no problem with them - given the choice between a 5 piece quarter sawn back and a 2 piece slab, I would choose the former although many folk would not. As long as you are confident about your joins I would go for the better wood every time. And the days of good quality 2 piecr backs in Rosewood are coming to an end - the quality of Indian is going right down. Younger trees are being felled and to make the width they are being cut off the quarter - the worst of both worlds.
The Angled 2nd brace - if this brace goes straight across the waist it will be too stiff and a dip can develop when the back swells (I build very dry) So it is partially to allow a little more movement which can help avoid distortion and splitting, also by making it more flexible (longer and lower) the bass response seems to be improved.
Finally, I scrape the binding then seal with glue and scrape again to fill small gaps but mailnly to prevent Rosewood dust from dirtying up the white during final sanding.
Hope this all helps.
Nigel
http://www.nkforsterguitars.com