Regarding coolant loss - As the engine comes up to operating temperature coolant expands from the pressurized engine/radiator system into the over-flow tank. This will cause coolant vapor (not liquid) to be vented overboard from the overflow tank as the liquid expands into it. At engine shut down the coolant in the pressurized engine/radiator system contracts as it cools down and creates a vacuum which draws coolant from the over-flow tank. Outside air replaces the coolant volume drawn from the tank.

As this cycle is continually repeated coolant is lost through the vapor vented overboard and must occasionally be replenished. You may sometimes notice a "sweet" smell, kind of like maple syrup in the area of the expansion tank just after engine shut down when coolant system pressures reach maximum. This is the smell of hot coolant vapors.

Additionally, there could also be some seepage of coolant from the water pump seal which would be normal.