Frameless mirrors/floating mirrors are hard to do when you have to hide a screen and possibly a pi/other hardware. (And you probably want polished edges for that to)
If you are able to build the screen and pi in to the wall itself and then mount the mirror flush on the wall, that would be one way of doing it.
But since your glass won’t cover the entire screen (being 1.1 inch to short) the best thing to do is to build a frame with a larger bezel around the mirror+screen.
And in that case yes, cutting the glass down would be good (just to get closer to the screens image ratio).
With a larger bezel you can hide the overflow and you won’t get a backlight-edge visible on your mirror (since all the visible mirror surface will have the screen behind it).
You could probably find a ready made picture frame that is close to your measurements, and then just build a simple wooden box around the components that you can mount the frame to and in the same time get mounting to hang it on a wall.
(something like this maybe : https://www.amazon.co.uk/14x10-PICTURE-PHOTO-FRAME-Black/dp/B00BTBGGFC)
You don’t need any specialized tools to make a frame (a saw, a hammer, some tiny nails, wood glue and some wood.)
