You are welcome to Google, but I first learned about the 18-seat limit for prepared foods shops (which are most coffee shops…) via this Wash Post article from several years ago.

“Their business was categorized as a prepared-foods shop, limiting it to 18 seats, but the space could hold much more.”

I could be mistaken, but I’m pretty sure DC zoning limits seating at coffee shops to 18 seats as they are classified as prepared foods shops. This applies to places without a kitchen / full menu of food. If a place serves food and has a kitchen, they are entitled to more seats.

Since you’re female, coming from Europe (I.e. no furniture, etc) and only staying for a year, this could also be something to consider. https://tmhdc.org/

You could even do this temporarily until you find a room. Probably cheaper than Airbnb.