I like the idea, but I think you should keep the same set of questions for everybody. The only one that seems to be personalised is question 4. The rest could be answered by everyone. If people know what questions are in advance you will probably get more interest as people know what to expect and whether they'd be OK answering them. It will also be interesting to see everybody's answers to the same questions. Maybe people could propose another one or two questions that can be asked.
Having the same set of questions is good and I agree with you that the participants in the interview should answer personalized questions directed to them since not all members here are posting in the same board or doing the same thing on what they are doing in the forum. This allows you to see their perspective on their role in the forum. Having personalized questions for DT members, or Merit Sources, and people active in their local board should also be considered as they definitely have other questions to answer set on their perspective.
You could maybe have the same set of 15 questions for everyone then maybe 5 personalised ones or something. zasad@ said he'll read through the last 100 posts of someone but you can't get an accurate picture of them as a poster just from that, or the posts will be based on those few rather than your entire history. If the questions are different for everyone then one person might get a really good set of questions whilst another might not, or might not want to answer half of them if any at all. Personally I would be fine with the questions in the op but there are certainly questions I wouldn't want to answer or have sprung on me. If the questions are all the same anyone can just write up their answers and either PM op with them or just post them here and the op can link to them. Having a set of the same questions will give you everyone different perspective on them as well. Think of it like the Proust/Pivot questions all the actors used to get asked on Inside the Actor's Studio.