That sounds big!!

The measurements of the post pack are approx.

10-17 cms wide (bag tapers).

15 or 19 cms deep (expands)

27 cms long

No, afraid not. I am UK 11 also & have just tried them. The pack is a good 2 inches shorter than my shoes.

It includes a seatpost mount with two different diameter rings. Don't recall the name of the adaptor but I bought a spare one at a later date in order to use the post pack on both my bikes.

This attaches straight to your post, nothing extra is needed. There is a small (secure) bracket which fits to your post and then you clip the bag onto this through a metal wire frame which loops round the bag.

Not sure....The measurements of the bag are 10-17cms wide (the bag tapers), 27 cms long and 15-19 deep (depending on whether the bag is expanded). It depends on how wide your lock is. Hope the measurements help you decide!

yes

It comes with two different attachments for two different diameters.

It fits to the seat stem, not a rack.

I weighed mine at 550g (including my back light which is attached to the frame!). It's very light when empty!

Dimensions: It tapers from approx 10-17 cms wide, is 15-19 cms deep, depending on whether it's expanded or not, and is 27 cms long.

Yes, my seat post has those measurements and it's fine.

I have clipped a cateye back light to the frame of the post pack. It seems to work well, though I check from time to time that it hasn't slipped round a bit.