I am on a UA Codeshare on BMI metal and do not have seat assignments. I imagine I will be in a middle seat somewhere in the back regardless, but any idea on how I can try to get a seat?

Also--and I am pretty sure the answer is no--with the way the ticket is structured (LAX-LHR in V and LHR-AMS-ORD-LAX in B), does my one-way upgrade (15000 miles) also apply to all segments or just those on UA metal?