For point 3 - there is a very good fish and chip place on strutton ground called the laughing halibut - i suggest this because its about a 5-10 min walk from westminster abbey. Unfortunately i've just checked on google and it appears to be closed on a sunday.
However,if you are going back via paddington then think about Hobsons - its a brand new takeaway and restaurant which i havent tried yet as its only been open a couple of months and i've been away most of the time.
http://www.hobsonsfishandchips.com/about/
It has good reviews on google and replaced one of the better F&C places in the area (Mr Fish) which closed when their lease expired.