Production-Standard General-Use Microcontrollers?

There are lots of production grade variants out on the market that do this already.  Most can be bought out of China via aliababa or Amazon for next to nothing.  Did you check with them to see what vendors are selling their micro for end-use such as yours?  Rolling your own board de-risks future changes that might come at you if you've integrated someone else's product into yours. Then your cert or validation from FCC is no longer technically valid -- that's where it gets messy.  

Other options are generally taking the existing reference design package and having it fabricated and assembled under your control.  I suspect that is an option you should look at.

Have you looked at the Mickroelectronic click board offerings?

You may want to take peak there.

https://www.mikroe.com/

(I am a very new newbie newb)

So it's my understanding that something like the ESP8266 is meant only to be a development/prototyping board, and that traditionally, the next step would be to design and manufacture your own PCB. However, my design is incredibly simple, only requiring wi-fi and the ability to control approximately 300-400 individually addressable LEDs.

This would be a  currency converter small volume product, and I find it difficult to believe that something so simple requires custom-made PCBs. Is there such a thing as a general-purpose production-grade microcontroller? It seems to me that if you can create something like an ESP, you should be able to create something similar that meets the standards necessary to be safely included in a commercial product.

Thank you for the help...