Sorry, yes, I was lapsing into FCP7-speak. Export Media... is the way to export a full quality video using whatever settings your Timeline is in FCPX. You won't be able to get any better quality than that for your export. I use ProRes 422 but not 422HQ. If your Timeline is HQ then fine, but I don't think there's any advantage to using a higher quality setting than your Timeline.
In FCP7 it was noted that Export Using Compressor Settings took longer than Exporting Movie... and then using that in Compressor - or do I have this backwards? - Tom can probably comment on this. Don't know if there's any difference in X. I don't know Chapterit, but if you're taking things through Compressor, why not add the Chapters there?
One other quirky iDVD thing - when you drag in a movie it defaults to the file name as the "button" or label text. Of course you can change that. I've learned that making that button text very long can cause the disc burn to fail. I don't know what the limit is, but I've seen burn errors go away by simply changing that text to no more than one line of no more than 3 or 4 words.