We made the decision to scan all of our old records. As I have posted before, that partly reflects the OCD side of my personality, as well as the nature of my practice. As a gastroenterologist, a significant number of the charts were not large, but it was important to have quick access to a colonoscopy or other report that might be 5 or 10 years old. We scanned all of the charts, generally "thinning" useless material and either importing the rest as a single batch, or in a couple of categories.
It felt really good to: a. shred and dispose of all the old charts, and b. know that I had quick access to all of the old information.
Yes, create pdf's, and yes, use Updox.
Having said that, I think that many people who are new to an EMR worry too much about how to complete these steps. There are several approaches described here and elsewhere. Pick the one that sounds right to you, and go with it. In my experience, it is unusual to hear people say, in retrospect, that they wish they handled their old paper charts differently. The decision probably doesn't really matter as much as it seems to matter to you right now.
One other point: Marty and David bring up the issue of large imported items files slowing AC. I think that this is a real issue, and I have worried about it. On the other hand, I believe that it is not a common problem, and while the size of the imported items file is one of the factors involved, it is not the only one. I think it is prudent to use a fairly small resolution for scanning (e.g. 200x200) but I do not think it should deter you from scanning old charts into AC. Just my opinion.