A: 301 redirect is the way to go
My Thoughts: It tells Google you want to use this URL but you want the other one indexed.
A: John says they work hard to prevent it and you should not worry about that
My Thoughts: So basically the answer is YES, but Google can spot these and correct teh issue. The best thing to do would be to open a thread in the Google forum if this happens to you.
A: If it is a manual penalty you will see a message in Webmaster Tools, if it is algorithmic you will not be notified.
My Thoughts: Google is very bad at handling this issue, if you move your Webmaster Tools account the messages do not follow and if you clear your messages the only way to find out is to send a reconsideration request to see what response you get.
A: Yes, disavowed links are treated as nofollow links and WMT Links to your site show both follow and nofollow
My Thoughts: Google still needs to address this area so that it is clear what links are dofollow and nofollow and what ones are already in your disavow file.
A: Work to have bad links removed even if it was done by a competitor or use the disavow tool.
My Thoughts: John hints that using the disavow file will make it so those links will not eaffect the search results.
A: Google are still experimenting but it is not a primary ranking factor. Many social sites create links as well and any boost to your serps may be from that instead of the social metrics themselves
My Thoughts: John still hints at the idea that links are the primary ranking factor
A: John says NO, Google does not have a duplicate content penalty.
My Thoughts: I think the question should be is there a devaluation for duplicate content rather than penalty. Google likes to make it clear that there are not many penalties but does not suggest wehn questions come up if there is a devaluation.
A: No Google does not use that at all for search
My Thoughts: Google may use it for search in a negative way, it may inform Google of terms you are trying to rank for.