Modernized Townhouse with Garage in Prime Williamsburg   469 Grand Street is a fully renovated, impeccably maintained two-family townhouse offering rare amenities and generous outdoor space in the heart of Williamsburg. Set on a quiet stretch of Grand Street, the sun-filled facade welcomes you into a 19-foot-wide, three-story home with a private garage-one of the most coveted townhouse luxuries in New York City.   Configured for both lifestyle and investment, the home includes a beautifully updated two-bedroom rental unit on the garden level generating $3,500/month in income, while the upper floors comprise a spacious three-bedroom, two-and-a-half-bath owner's duplex. A large terrace off the kitchen leads to a deep garden-perfect for outdoor dining, entertaining, or simply enjoying the seasons.   Built 65 feet deep on a 95-foot lot, the property offers 2,343 square feet of unused air rights, allowing for future expansion. The location is outstanding-just moments from the neighborhood's top restaurants and within close proximity to both the L and G trains.   This is turnkey townhouse living at its finest-with every detail already in place and the flexibility to grow.