Judging from the blueprints, it doesn't seem that there will be any line of sight into Diagon from the London waterfront. There should be more layers of wall coming to that entrance.
There will be... we saw the last central arch column laying on the ground in lastashen's photo. There is so much stuff going on with ramps and such that I am not sure where the buck stops. Enter here, go there, walk around and around there until you are somewhat back here which by then will be hidden from view. It's very interesting yet odd and confusing.