> Will the stand or cradle (dock) scratch my desk?
No, 3M rubber strips attached to the both stand's "legs" & cradle (dock) protect your desk from scratches.
> Will the stand support 5K iMac Retina, 27" iMac or Apple Thunderbolts?
Yes, the stand is compatible with 21" - 27" iMacs, 5K iMac Retina and Apple Thunderbolts monitors at Rear insert position; and all monitor up to 32" at top placement position.
> How do USB 3 & Audio extension cables work?
We include two high-quality USB 3.0 cables and one 3.5mm audio cable in the stand set; cables are directly connected to your iMac or Thunderbolt USB ports for best capacity.
> Will the full size Apple keyboard with numeric keypad fit with the stand?
Yes, the "nesting" area under the stand is wide enough (470mm) to store a full size Apple keyboard with the numeric keyboard.
> Will the Mac Mini or Macbook Air and Pro fit under the stand?
Yes, the space under the stand is big enough to store a Mac Mini or an any size of Macbook air, Macbook Pro.