How Do I Say "We are going out for drinks" "We are going out for a nice meal"

Can We Sit Outside? Can someone tell me if the correct way to ask a waiter if "we can sit outside" is "Possiamo sedermi fuori"?

When to use avete Can someone please tell me when "avete" should be used instead of "ha". I had read that avete should only be used when talking to more than one person is this correct?

To Say we have arrived do I say Abbiamo ARRIVATO or Siamo ARRIVATO?? So if I phoned someone to say we have arrived would I need to say "noi siamo arrivati" or do I drop the noi?