The reference to a “a house… prepared… for man” means exalted man, or any kingdom of glory (D&C 88:21–24). At this point, Moroni makes no distinction among the various kingdoms.
Reference: Joseph Smith has obviously reached for familiar language from the King James Version to explain the concept on the plates. John 14:2–3 includes the house, mansions, and Jesus’s preparation of the way:
In my Father’s house are many mansions: if it were not so, I would have told you. I go to prepare a place for you.
And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, there ye may be also.
The verse in Ether emphasizes the function, not the place. In John, the place is the reward. In Ether, the place is the promise of celestialization that fuels our hope and faith. In Ether, the house is the goal hoped for. In John it is a promise obtained (or obtainable).