Wondering what would be the best / cheapest option to upgrade from Economy to Business : by auction / SeatBoost or at the Gate just before boarding. Flight is tomorrow / Saturday BOS to FRA.

Also if I have a BOS-FRA (Condor) and then a connecting from FRA-Stuttgart ( in Lufthansa) on the same ticket, do I have to re-check baggage at FRA , or will it be through checked in to Stuttgart?

For immigration into Germany, can an. US citizen get in the EU line? In some airports, I have noted that along with EU countries, there is a US flag.