you will be staying in the same terminal. The Air China lounge is pretty underwhelming. Priority Pass gives you access to the Air China First Class Lounge which may be marginally better. There should be a shower. I know there's a pretty good Cathay Pacific Lounge in the terminal but not sure you can go in w/ a CA ticket.

Last time I was there PEK merchants do NOT accept foreign currencies and i doubt this has changed, so make sure you have either yuans or credit card. You can find chain restaurants in the terminal like KFC or Pizzahut, and (probably) mcdonalds.

PEK also has pretty poor environmental controls. It's annoyingly warm in the summer, and pretty cold in the winter.