We don't have as many rooms as you do & aren't nearly as busy, but payment at check-in works for us too. It's less disruptive to my routine for some reason. While I run the card, they sign the registration form agreeing to the policies and can also pop into the restroom right there. They also have all the brochures to look through plus tapes/DVDs. I think it works because I'm only steps away right inside the door in our office/den & I can still chat with them. It's just what's comfortable for me & helps me to stay organized. (such as it is...haha!)
However, I've had a couple of experienced B&B travelers that seem surprised at that & I play it by ear with them. I'll just say, "You can bring your card back to me to run when it's convenient for you." I haven't had to chase any really. Usually, they bring their card to breakfast on the day of check-out. I think this is because there must be a lot of B&Bs that accept payment at check-out or they've taken a deposit at booking & take the balance at check-out..