Fabe, True. If you have a working toc in your mobi file after Calibre conversion it will remain intact after KDP conversion. It is what you might have heard referred to as an "inline TOC".
BAZ, my old matey, I'm not entirely sure what you mean by linking your index to html sections? If its already passed muster, you should be about done. Either way, if your nervous always use a copy of your file to "play" with things. In fact you should always do that anyway. Just "save as" and add 01, 02, 03 etc to your files as you go.
It will save you a lot of time trying to figure out what you've boo-booed.