Hi mattsuzie,
here is a picture of the 420 drain plug. If memory serves me right, it is a 13 or 14 mm plug.
I doubt it will come through that drain as Murphy's law just won't let it happen. To take the oil pan off is not too difficult, there are only 2 bolts that go through the pan that have nuts on top as they hold some tubing from the transmission going to the cooler. Driverside. You need to take those 2 nuts off first, otherwise the bolt might brake off. I know from experience.
The hard part is to not overtighten the bolts upon installation. You need a new gasket (about $16?) and a torque wrench in inch pounds rather than footpounds. It needs only 8 ftlbs and my torquewrench was not sensitive enough. You can see the split gasket in the picture. The pan holes will get bent and you have a leak as a result of overtightening.
You will need 8 liters of oil.
Good luck
Reinhard Kreutzer

This shows the oil pickup filter in the pan, that the foil might clog with the resultant oil pressure drop as moedip explained.

Gravity--possible, but it would have to get past the 8 valve springs and rocker arms first. Oil pan isn't bad to remove, but the 4 bolts n the valve cover are easy and the gasket can be reused. I'd look there before even draining the oil. Not that draining (and changing) the oil is a bad thing.