What to check first?

[jonesg]

I'd say its a bit damaged by now but get some oil in it and leave the dipstick loose to prevent crankcase pressure, it'll probably run better ...eek!
Look for the oil leak, pop the plastic (top) timing cover and look at the belt.
Look for oil puddling around coils , oil can blow past oil filler cap.
Look at the lower crank area , the back ends of the cam shaft covers.
If its turbo check the oil drain pipe.
Hopefully its not the rear main seal.

[abscate]

You probably area couple liters down,but drain it out and in fresh

Fingers crossed