Assuming I fit my Alpine into this car, which im not sure if I will but it's quite likely, I can offer some advice on mic placement.
On my SEAT I wired the mic behind the dash, and all the way up to the pillar to the top right almost next to the driver side window.
It was good, but easy on the SEAT, the Golf looks a little trickier to attempt that, so may just put it on a bit of velcro, and attach it to the dash (almost to the area where you would rest your knee)
They are pretty good mic's to be fair, so anywhere nearby will be a good bet.
As for box, put that in the glovebox too, saves space and the wire they provide for the mic is usually plenty long enough for other placements.
A few folk put the mic up above by the rear view mirror but that's a bit involved if you ask me! :p