I would assess how everything is organized. Usually there was a system to how it was done in the past even if it seems chaotic. Then outline the commonalities of documents into a list. Then, consider how those documents fit into the existing company structure or processes. This may consume your time, but I’ve found that historical documents, how they were handled, and what records were kept are often an eye-opener to the current structure/past owner. I wish I could tell you this is fun work, but it is not. However, the value I’ve found in doing it is often worth a lot more than the pain. Once you are comfortable understanding the big picture, digitizing should be easy. Then, have someone else digitize it, but give them the structure you want.

You can hire freelancer outside the US (e.g. Latin America, India) that cand do tha work cheaply. Have done something like this in previous jobs and they are efficient (also works if they have to type the information).

A important thing to be aware is to have specific process/steps of what they should and where they should store the digitilized information otherwise the end result can be messy.