I would definetly remove the extra fluid. Too much can cause damage. As for the stripped drain plug in the pan, I would first see if a new one is available. If there is, then I would use a drill bit that is smaller than the diameter of the drainplug and drill a hole through it. Use a tap and die set and unscrew the remains, then install the new one. Actually if you have a reversible drill, drill it that way. The force should free up the plug. Again, though I would first get a new plug.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member