I'm answering part 1) partly to bump, partly to add what I know. Grapefruit and bergamot are popular opening notes for many scents: bergamot more so than grapefruit. In believe in each case, the extract comes from the rind because it's plentiful and easily extractable. That said, grapefruit is trickier than bergamot because in some cases grapefruit extracts and compositions can turn sulfurous on some skins. In any case, both grapefruit and bergamot are fleeting. Some flowers don't frequently get extracted because they are fiendishly difficult to get right: methods of extraction vary and either get only a partial picture or worse, mutilate the essence. Rose is a very popular note in perfumery, but I've never smelled any rose composition that got it right: they tend to the cartoonish. There is a scent called O Pomelo, from Comptoir Sud Pacifique. It's apparently quite good, but fleeting, to put it mildly. I would not recommend you buy blindly, because CSP does tend to be either cloying or strange. My Vetyver Haiti starts with a mustard note. Mustard. wtf. Thanks, Thomas. I might have to blind buy O'Pomelo. I read somewhere that the note is extracted from the pomelo flower, but I see no way that they can get it right. It's spring my way and I was in the yard earlier just standing and sniffing the pomelo tree. I can't begin to explain the brilliance of it.