Help! Should I just do the Gloabal pass for convenience?

Edit Subject

Hello - we are traveling from the US to London on 12/19/2018 - we have booked a train to Brussels, then a flight to Munich, will need a train to Nuremberg, have a flight to Paris and then train from Paris to London . We leave back to the US on 1/4/19. What's my best option? There is a special on Global Pass right now - is that the best way if we don't know how much we are traveling in each city?

Thanks!