A:Answer One can adjust the size of the opening from ~ 4 7/8" to 7 3/4".
One can adjust the mount to hold your tablet in either a landscape or portrait mode. If you want to rotate the mount, I would do so, before attaching your tablet. The screw that allows you to adjust the width is also used for the rotation. If you mount the tablet first, then rotate, I'd be concerned about the tablet falling off. If your tripod head allows for rotation, you could do it there as well.
I mount my iPad in landscape mode, since I'm uncomfortable using the mount in portrait mode. In portrait mode, the mount grips the tablet on the sides, but there's no support at the bottom.