Yes, GeoJSON coordinates are longitude and latitude in degrees and that's how I treat them in MFCG. But it doesn't really matter unless you are placing loaded data on the actual Earth sphere, so in the future I'm going to switch to much more readable values in meters.
Road width is not a coordinate, it's obviously a length value. Its unit is a length of a degree at the equator which is around 111 km. The width of major roads in MFCG is 8 meters.