Andy,
All very good questions…
It is very professional to tell the client that you can’t give them a final estimate until you’ve actually “reviewed” the material. I wouldn’t be quite as specific, such as mentioning the words “additional editing,” that could freak some people out. Just tell them that its always your practice to make certain that all technical considerations have been taken into account, so they can be assured that their final product will be as good as it can be. And yes, give them an estimate with a range that covers what you believe to be customary, and tell them you’ll give them a firm price when you’re certain of what’s actually required to complete the job.
Hope this helps…
Good luck,
DRW