Would highly recommend the Cologne Marriott - it is very new and one of the better Marriott hotels I've stayed at in Europe. Only about 3-4min walk from the train station.

I much prefer row 16 instead of row 7 if it's available. The area in front of row 7 can get fairly busy during the flight with people wandering around. Row 16 has loads of legroom, and tray table extends from the seat in front of you (which doesn't recline, meaning that space is always available).

Go for 16DEF if possible for the return flight CGN-EWR or you'll have direct sunlight blinding you any time you lift the window shade.