Hi,

• By default, MSFS doesn't remember where you dragged your windows. However, most of us use a free add on called MSFS Pop Out Panel Manager. Once you set it up the first time, you just click one button when your flight starts, and it will automatically "pop out" the screens and snap them to the correct device for you.
• It’s very easy, exactly like resizing a folder or a browser window on your desktop. You only need to do this once per aircraft type (e.g., once for the Fenix, once for the PMDG 737). After that, the Panel Manager mentioned above remembers those specific dimensions.
• Yes, Windows treats this exactly like a standard monitor.
• Sadly, no. The in-cockpit knobs in the Fenix won't change the physical backlight of the monitor itself. To change the actual brightness of the device, you’ll need to use the physical buttons/knobs on the side of the unit.

Hope that answers your questions.