Combine and deduplicate three documents

I have previously had some market research carried out by three people all submitting their responses as a Word document, with documents returned to me as a combined total of around 360 pages.

The market research was all about how the Building Codes work in a number of countries.

I would like the three reports combined into one, all indexed and with a table of contents and a consistent layout. The reports should align reasonably closely, but there are parts in one document that aren't in another, for example. The freelancer may need to carry out a small amount of primary market research in order to fill in some blanks, or at the very least to make a comment that the information is missing.

The three reports are in slightly different styles, so it needs to be aligned. The freelancer will need to use the correct Document Outlining tools to allow a consistent table of contents.

I think the end result needs to be something like this:
Introduction and Purpose
Country A
- Country Statistics
- Overview of compliance regime in place
- Regional variations
- Specific requirements that we need to be aware of
- Useful contacts
Country B (all in alphabetical order)
- etc.
An overview of the countries it would be easiest to get into
An overview of the countries it would be most difficult to get into