Going clipless and which shoes?

Couple of points, always try shoes on when you've been on your feet a while as they do swell a little so when on a long ride those shoes that fitted in the shop on a cold early morning will be a little bit too snug and there's nothing worse than a bike shoe that's too small!.

Most mtb/spd shoes are fine in the width sizing (I actually bought Lidl shoes as they fitted my wide feet perfectly & they were well made & cheap!)
Road shoes vary quite a bit from manufacturer to manufacturer but I'd say go for one size bigger than your standard shoe size as a starting point.

I don't agree with this last bit, and I hear loads of people saying size up with sidis they run really small etc -cycling shoes are supposed to be tight. I wear a 10 in street shoes ( Crockett and Jones or Converse) I wear a 44.5 in Sidis and these fit like they should, a snug fit with almost no toe room.
Trying shoes on when your feet are swollen from a days walking riding whatever is definitely good advice