Backlight always on makes sense to me when you think about larger modern bikes with digital displays, the backlight is on all the time along with sidelights / running lights. The switched live on yours just turns on the display, which the backlight is part of.
It may have the ability to run without backlight but maybe the default until you've wired in light signals is for it to have the backlight on?
For the fuel and gears, you'd need to add in a fuel sender/float (almost impossible I'd think with that tank) and a gear selector sensor thing along the lines of what
@Malt_Vinegar did with his bike, although he replaced a neutral indicator switch with a gear indicator switch of the same fitment (but extra wiring).