2 - And add USB connector support
Normally the easiest way is to use a USB to serial chip, However those are tricky to solder so it is normal to add a USB to TTL serial board or module. You can get them in the Store, link at top of the screen, or from lots of other vendors.
You face a problem if you want to program up a processor to do this because again they are in a package that is difficult to prototype with. Alternative you can use a processor like the Leonardo and copy that code into it.