Just as a suggestion, I'd look at the Pro Micro. Same price, better (small) form factor, USB support is built in,
No need for a shield, just use one for prototyping on a breadboard then solder directly to another board once you are happy with your wired prototype. Just be sure to order the correct voltage for your application (3.3V or 5V).
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Only reason I suggest these is because it's so easy to cram it into whatever space you have as it is less than 25% the footprint of an Arduino UNO.