Not trying to be a party pooper at all, but reality beckons.
You obviously know what you're doing AFA construction goes. Framing, drywall, electrical, gas, etc. Looks good to me. But in most towns/cities/states you need not only a permit to do the work, but it must be inspected/certified as well. Also, if someone is living in the new space, zoning and fire safety laws etc come into play.
Long ago, I checked with the town supervisor - if I'm not increasing the square footage of my property, nope. We had some friends from Long Island come for a visit a few years ago. It blew their minds that people around here have a right to work on their property.
