I am looking for the supplier that will burn for you. How many KB PCBs do you want? JLC does 3 minimum and I only need 1. I actually tried loading up the files and it was pretty simple via JLC. I also checked out OSH Park, but that was way more expensive, but I suppose much quicker to get.
To keep it centralized, the MCU discussion is in the other thread. Which I see you have already found. TL: DR, both are options, but I was leaning toward Microchip doing the programming. But if I find a cheap enough tool, I will program blank chips.