If you loose every run, you will still shoot some where in the neighborhood of 600-700 rounds. If you are winning, depending on the size of your squad, you could eaisly shoot over 1200.
No, you cannot retrieve your brass. They do make the squad pick it up and put it in buckets before moving on to the next stage. They have large tarps next to each shooter so dumping it in the bucket does not take very long. Only the shooters with wheel guns keep there brass.
I believe there are 15 total stages in the match.
Hope that helps!!!