1. I don't think there has been any (?) demolition work yet. Yes, it could possibly upset the gorillas but also the whole site seems to be mothballed until its clear just how its actually going to be used and a/the developers move in.
2. They have posted previously that the gorillas do still see some other people apart from the regular staff. I don't think any VIP experiences are offered there, that is for booking them after they move.
3. I believe this is to allow them to settle and for introduction to the Mangabeys etc to take place. My own opinion is that the adults will not have been stressed by these changes- either by the sudden protracted absence of visitors or their sudden return when they are on show again. As gorillas have good memories I think they will just take the change in their stride.The two male youngsters who have grown up so far in a very quiet environment, might notice the difference intially.