Hello,
The recommended screen resolution is 940 x 540 (a 16:9 display)
but the emulator works on absolutely any resolution by scaling up/down the render on screen.
The entire area screen is usable for your custom template (see the screenshot).
it's recommended to maintain the aspect ratio by using a 16:9 display but there is an option in VDASH-EMU settings to fit the entire screen.
Here are some different displays using the VDASH-EMU:
Tiny Android 16:9 screen:

5" Android device (notes: full area of screen is used for displaying the telemetry):

24" PC Monitor:

Cheers,
z