normal lang na may consumption nang oil, 500ml during the entire 5000kms is still OK... especially if the vehicle is driven for long distances around a steady pace of 80-100kph.... by the way whats the odometer reading on your vehicle? theres really no problem in switching between viscosities, but i personally like to use 15w40 during the summer, then revert back to 5w40 during the rainy days.., oil could be lost in many ways not only through your tailpipe or visually through your exhaust.

there's an oil recirculation mechanism for the blow-by gas, there could be tiny leaks in your oils seals both front and back, the gasket and oil could also be an outlet for oil moisture to get out...

oil consumption should really be minimal unless you're running an engine through its BREAK-IN period, during this time the metals are still setting in...