Hi Mark
Without customising anything with Toolset, by default you will have a post archive for your documents CPT, where all document posts are listed, at a URL of site.com/documents/.
You will also have taxonomy archives for both letters and reports. The name "taxonomy archive" can be confusing, because it lists posts, posts that have the term of the taxonomy in the url assigned to them.
I don't know what the terms of letters or reports are, let's say "alpha", "beta", and "gamma", and "one", "two", and "three" respectively.
So at the url site.com/letters/alpha/ it will list all posts that have the term alpha of the taxonomy letters assigned to them.
At the url site.com/reports/two/ it will list all posts with the term two of the taxonomy reports assigned to them.
(I'm using documents, letters, and reports, but maybe the slugs are actually document, letter, and report.)
So, unless your settings for the post type and taxonomies disable archives, then those archives exist already (and will be output according to your theme template files).
With Toolset you can then customise them (at Toolset > WordPress Archives), both the appearance, but you could also add filters or change the order to order by post title rather than date, for example.
