There should be 3 maps side by side, with the camera always on the middle map. This way you never see an edge unless the camera is at a very high altitude. Just one map instance, but mirrored in 3 places.
Signed longitude has been the convention for quite some time. Prime-Meridian 0, positive East, negative West, Anti-Meridian 180 either direction.
Heading convention has been unsigned 0 to 360 deg. However I believe signed heading makes it easier to quickly figure out direction. Just by the sign you immediately know if the heading is east or west. Just by the magnitude you know how far off it is from north.