You might think they're galvanized but they still rust and its the biggest problem, see any in the B posts, screen gutters, front wings(headlight), sills, etc, etc. Main area is the kidney bowls, don't mess around raise the rear wheels and remove them and have a real good feel right up into the arch towards the doors, they can seriously rot there and it isn't cheap to repair. At £9-10k this will be a danger area for rust, but you might be lucky, I looked at cars up to 15k and some of those had rust. Bad paint on the bumpers isn't really an issue other than cosmetic as they are made from ali.
Having a G50 doesn't necessarily mean 'no problems' its should still change smoothly and easily whatever the gear.
You want to see records/evidence of maintenance, regular oil changes, who's done the work. Puff of smoke on start up is fine, although is should disappear after a few moment.
Don't rule out an SC, they're often better value and will virtually match a 3.2 anyway.
I'd seriously think about having a prospective car checked over by a professional if I were you.