I am unaware of a "nice and quick" way to get metadata information describing all this detail about fields in the data source.
In case the brute force path is not already apparent to you, you could of course open each workbook in Tableau, right click on each data source(s), and choose edit connection.
I'm pretty much only familiar with SQL Server connections, but from there, you can see the server and database, and then evaluate the table, multiple tables or custom SQL that generates the data source Tableau uses build to build the extract. (aliasing can be done at this step that will make the field name different from the name in the underlying database.) For other data source types, I assume something similar is possible.
Within Tableau, you can also check each field to see if there are aliases and also get data type, null allowance, and domain members.
(I am familiar with version 7, so if you have an older version you might have to follow a different path to these items)
Aliases: Click on the Data menu, select your data source, select Edit Aliases
Field Description: right click on the field and select "Describe."
Not an ideal solution, I know...
I'm interested to see what other responses you get, as we could stand to document our Tableau workbooks better in my own organization!
You can use my tool which automatically pulls workbook from Server and prints field definition. Everything done in JS and in browser.
Step by step instructions here: