If it's an REO, the bank already owns it. It went through the foreclosure process.
That means that you should be able to get access to it to inspect. So 1) is not an issue. 2) Yeah, don't go to that area. 3) Should not be an issue, liens should have been wiped during the foreclosure process, super priority liens aside - either way you'll have a title report done and get title insurance. 4) something you have to research, but that's usually not an issue - potentially much more of one if an HOA is involved 5) again, see #1.
Not sure why you'd attend an auction when you're talking about buying REOs - are you buying at auction, or are you buying REOs?
You say REO, but the way you describe the problems make it sound like you don't have any due diligence, more like an auction, but you say "that didn't sell at auction" but then you say you'll go to an auction. I'm not sure you're clear on what you're planning, so it's hard to recommend books or further reading. Please clarify and we can potentially help more. :)