Hi Liz, Harvest Inn (St. Helena) has some beautiful views of the vineyards, and certainly seems like they could accommodate a party of 20. They have some beautiful photos on their site for inspiration. The Napa White House Inn, photo below, could also be a great idea! As far as restaurants, I'd definitely look into Fume - they have an outdoor patio that could accommodate 20, but also offer catering as well. Let us know how the planning goes!! I've featured this on the homepage, would be great to hear more information about past Napa weddings.