Song meaning of Ada (Live in Brussels) by The National

Oh boy, where do I even begin with "Ada (Live in Brussels)" by The National? This song is like a riddle wrapped in an enigma wrapped in a snuggie. Is Ada even a real person, or just a figment of lead singer Matt Berninger's imagination? Probably the latter, but that doesn't stop him from giving her some bizarre advice. Apparently, Ada needs to put the sounds of her house in a song and then try to be speechless for a minute. And if she faints? Just go out in the hallway and let everyone have her neck. Wait, what? Then there's the line about standing inside an empty tuxedo with grapes in his mouth, which I can only assume is some kind of metaphor for...something. Honestly, I have no idea what's going on in this song, but I know one thing for sure: Ada better watch out for that lake, because it's going to have a nervous breakdown and fall into a thousand pieces around her. Yikes.