1. Standard load rating in the us is 40 lb/ft^2. You have about 3000 pounds. Is the foot print 73 ft^2? (ie 5' x 15'). If not, you are over rated. You can build a platform that increases the footprint in most cases.

2. I would make the seller fix that. You don't want water going where it should not. Check the downspouts while you are at it. 5 foot to fall away minimum.

3. If there is not a code violation, there is not an issue. Just don't think you are going to plop a hot tub on it.

4. Would be pretty surprised if rough framing passed inspection missing hangers. You can call the building inspector for the local AHJ and ask him to make a determination if you need a permit to install hangers. That should get him out to take a look, and then you will know.

House inspectors are mostly scam artists (there are a few really good ones too), so don't get too carried away.