You can't go in to the real one. The real one was destroyed in 1687 when it was being used as a gunpowder depot(!), and then triggered by a mortar round.

They've been slowly rebuilding it over the last 50 years, but it's nowhere near done. It involves figuring out where each and every block goes, often undoing previous reconstructions. You won't be going inside it any time soon.

There are gift shops everywhere, of course, but I highly recommend the one at the Acropolis Museum (at the bottom of the hill). It does a great job of putting the site into historical and archeological context.

No, from what I could tell the greeks have tried to preserve the entire Acropolis as it was in ancient times. Unfortunately this means there is construction equipment everywhere as they are constantly trying to rebuild, at least when I was there.

Pretty much every shop/business surrounding the Acropolis is a gift shop, they all sell little souvenirs and stuff.