As a Japanese taxi-driver asked us in New York 14 years ago - "whherr you won go?" I answer "Quayside for the NCL Dreamward please. "Howw you get there?"
Only from being up the Empire State that morning did we know which direction in relation to our hotel that that HE should take us.
Airlines from Manchester cover MOST destinations. But if it's indirect to the USA do your plane change over there. It makes for a better return trip back to Manchester early morning. DON'T plan to change at Heathrow or Gatwick. You'll regret it.
You can fly from wherever you like if you book your own flights.
Yes- I believe Manchester still has an airport, though I am not sure where the planes fly.
It might help if you indicated to where you wanted to fly.