I'd imagine Harry will open up the Castle to be more of a community center for those who are Supernatural or Supercurious. Mouse for community outreach. Michael or Will for self-defense lessons. Basic classes (pamphlets? a web site?) on thresholds and circles and how to know when it's time to call in a wizard.
Turning his home into a business would weaken his threshold, and that's bad with the knowledge of the upcoming events. Everyone who visits would have to be considered guests by Harry, and be there overseeing the invites all the time and observing guest-right too.
He has enough on his plate.
If anything, he could support another location to do this....maybe his old office building location, if Marcone doesn't already own it.