This was the first time for me that I ordered an electronics assembly so I think I may share my experience. 

First of all, most of the credits should go to Ermanno Antonelli who spent hours and hours figuring out the component data sheets, designing the board and populating the components list. He generated a CAM output in Eagle and a BOM list in Excel. 

At PCBWay you have to make two orders - one for the boards and one for the assembly. I already had some ATMEGA328pb-au and also the RS485 chip which is not so available right now. So we chose the option where most parts are sourced by PCBWay and some are provided by us. Unfortunately, the TVS diode is not available to PCBWay and I didn't order it yet. So I will have to solder it myself. But that's easy. It is a big part on the back side.

Ermanno then uploaded the CAM files and the BOM as an Excel file. PCBWay wanted a certain format, so better use their template from the start, if you plan to order there. The layout was processed by PCBWay and cleared. I received an updated version of the BOM where PCBWay had marked components that had to be replaced and suggested alternat versions. In some cases it was just a difference in the format of the serial number. I had to answer in another column of the table and yet received an updated version from PCBWay for a final approval. The BOM issue was handled in a very effective and professional way.

With this settled, the final price for the assembly was calculated and I had to pay - with a generous sponsoring from PCBWay who like this project. We will offer boards for a share of the total costs including shipping and parts provided by us. This will amount to a total cost share of $40.

Finally I received the working file plots from PCBWay. I wonder whether PCBWay will allow me to make them public too. I will ask.

In any case I copied them all to powerpoint and compared them to the renderings of the board that Ermanno had sent me. They all matched. You will find the printouts below.

Ordering PCB Assemblies is actually not so hard - if you have Ermanno to prepare the files for you.