I would think as long as the home is secure, which it would have to be, they would be allowed the use of family pieces.
But yes for practical sense, a crown property or Cornwall property is far more practical. Honestly think where and which depends on their London home. If they plan on a major apartment in London, I wouldn't think they would have a large property outside of London. Likely a smaller country home. Something in the duchy of Cornwall would probably suit them size and security wise. The homes available at Windsor seem larger, and the ones at Sandringham would need to be converted back to single homes. If they opt like Edward and Sophie to have their main home in the country, then that opens more doors. A larger home at Windsor would be great, as it would be close to good schools the royals often attend, as well as London and other events.