Hi helpful people, thought I would let you know what happened..

SQ 11 arrived a little early, at the gate at 18:50. I was at the downstairs Keisei counter by 19:10, so I was easily able to get a ticket for the 19:30.

Changing at Nippori was easy thanks to shinjukuflyer's advice to be in Car 10 (actually I'd forgotten about that when I boarded, but when I remembered I looked up and found I was magically in car #10!)

I was on the street outsife Shinjuku at 20:25 and at the Park Hyatt about five minutes later!

Next morning I took the 07:05 Limo bus and was at NRT T2 08:25.

Thanks for all the help guys!