The patch lead I linked to is all you need and of course this mates up with your new radio wiring harness. If you already have an aftermarket radio fitted then it should be fitted into the dash opening with the adaptor kit. In the adaptor kit would have been fittings for single din, which I believe you have got fitted, and there will be also the kit for double din. If single din fitted then it would have had a cubby in the kit to fill the void, obviously left out if going double din.
Regards the Bose, which model Mk3 do you have? I'm not sure if the speakers are badged Bose on the Mk3, they were when I had a Mk2 with Bose.
Bose was in the option pack on some models so it depends if it was in the spec.
Facia kits look like this, although try other ebay or Amazon sellers for better prices.