I don't know if the Biltmore Estate was their main residence, but if it wasn't, I have to wonder at what would have been. Mum and I go up there all the time, mostly to deal with the winery, but occasionally, we poke around the mansion as well. The library is impressive, the rooms just go on forever, and the organ next to one of the dining rooms is on par with some of the grandest instruments in the cathedrals of Europe.
In 1912 there were many branches of the Vanderbilt family, and a whole catalogue of residences. The symbolic "head" of the family had his principal residence on Fifth Avenue in NYC between W 57th and W 58th Street, but the best known branch of the family, and certainly the social leaders, lived at Fifth and W 52nd. Directly to the south of them, between W 51st and W 52nd were the famous "twin mansions" built by another branch of the family. There were other houses of varying degrees of bad taste on 'Vanderbilt Mile' between W 51st and W 58th, but the entire complex has been demolished. The original "Commodore's" house on Washington Square North still stands and, compared to the later structures, is quite tasteful. A.G. Vanderbilt, lost on the Lusitania and often linked to the Titanic, maintained a suite in the Vanderbilt Hotel on Park Avenue at E 34th, which still stands 'though it closed as a hotel in 1964/'65 and had its lower floors unsympathetically modernized.
Dont really know. The Astors had a several-generation headstart on the Vanderbilts, and had invested, wisely and heavily, in NYC real estate, but the Vanderbilts made their fortune in railroads and transportation, which was hugely profitable. The Astors, until J.J. and his mother built that garish twin residence at 5th and E 65th, were certainly quieter about flaunting their wealth than the Vanderbilts.