Good questions. From what I’ve seen, most people have been able to use a U.S. credit card, but it can depend on the specific office or system. Some have had occasional declines, so it helps to have a backup card just in case. On fees, it’s usually more about your bank’s foreign transaction fee than anything added locally.
As for timing, a lot of people are being told pretty broad estimates, and in practice it still seems to vary a lot depending on workload and location.