My new PCB has arrived (see below) - it all looks correct ... but we'll see.  My next step is to place all of the sockets and make sure I didn't mess up any other measurements. I'll post when that's complete.

Also - I discovered that diptrace has the part numbers for the different components I'm using, and I can use those part numbers at digikey.com to order connectors which plug into the PCB.  For example, the connector I'm going to use for power can be found here:

https://www.digikey.com/products/en?keywords=52004-0310

The status.md on my github currently has a "parts" section with links to the parts I plan to order.

This will take a lot of the guess work out of finding the right connectors for parts of the board which require external connections.  But I'll wait to order those until after I've verified that my design is correct and the board works :)