Glad to help you!
1) As described by HTF, the bridge is there to support the transportation of Team Members, particularly those of the entertainment team, but we don't know specifics. It's also meant to emulate a bridge on which trains pass, presumably the Express.
2) It's entirely indoors. Clever lighting and hidden electrical stations will keep it dark, but certain sections will be well lit for guests to proceed safely.
3) According to Jim Hill (and furthermore the Creative team that led him around the construction site), the brick effect will very much be there, but we have no clue as to how it will be accomplished. The entrance is very narrow. It is all very narrow. Expect lots of queues, lots of return tickets, and if you're going in the peak season, lots of frustrated people. Plan wisely, and you'll be rewarded.
4) Both trains will look as though they're departing. The Hogsmeade Station has the main engine stop before it "backs out and heads to London". So, thematically, it makes sense. This is why both of them are facing south. The story has to match each time they arrive/depart.
5) Yes. We've been told it's just a lot of mirrors (take that either figuratively or literally), but I have some reason to believe it'll be more than that, at least thematically.