The one he will get hit hardest on is the taxes/IRS thing, because he has had somewhat conflicting/bad statements on it. This will be the toughest on him, I imagine. We already had a discussion on the meet the press and talked about this.
I wouldn't doubt the Don Black, old newsletter, prostitution, anti-drug war, etc will all be brought up, but Ron Paul is pretty damned good with those questions. The tax one is the one that will come out making him look the worst. I hope he answers right off the bat that getting rid of the individual income tax/IRS is what he would like to do, but the best he could probably accomplish is cutting taxes and perhaps reforming them because he will have to work with congress. I hope old statements on taxes don't come back to bite him in the ass. Seriously, I think this issue is the one that makes him look unrealistic. He has to handle this one well or he will be a laughingstock.