Can you buy a house with BTC? Yes! All you need is a buyer with coins and a seller that will accept them. The value of the transaction is as of the date of the contract, when the coins change hands.
You answered your questions already. As you see, there are so many patronizers of bitcoin who became rich and bought a house by gaining high profits with bitcoin. If it's possible for them, then there's no way we can achieve that, too.