Welcome to the Wedia Companion forums
To answer your first question, the easiest way to set XBMC up to recognise the paths is from within XBMC itself. Make sure that the folders containing your media have permissions that will allow XBMC to access them, this can be either simple filesharing or secure and need a username and password, then from XBMC Video Section select add source, and browse to your media folder(s) and add them. If you do use secure filesharing then the username and password can be added in XBMC preferences and will then only need to be added once.
As for your second, you still need to tell XBMC to scan for new content, if XBMC finds a media file with an associated .nfo, .tbn, and -fanart.jpg, it will use these files as its source and doesn't use the internet. This has 2 big advantages over scraping from the internet, (1) scraping from an nfo file located on a network is much faster than scraping the websites, and (2) XBMC will no longer get the wrong movie.
The only thing that the above doesn't apply 100% to at the moment is actor thumbnails, XBMC still needs to download these from the internet, the url of each thumbnail is stored in each nfo file so no scraping is neccessary, but if cast thumbnails are enabled XBMC will download these images. There is something in the works though, that would allow these thumbnails to be stored locally by Media Companion aswell.