All heights and widths are fine. It should roughly translate to the dimensions of a portable device, i.e. but not necessarily. So if you want to do it in HD that's fine!
From the rules:
Classic LCD-games are monochrome (exeptions being LED-games, in which case each figure must have one color), but it would be interesting how color versions could look like. If you work with color on a LCD-game, make sure that there's an option to switch to monochrome.
The main rule is that the graphics are fixed in place, and can only be switched on and off, but not moved. So it's definitely more than the art style .... It's a philosophy (joking!)