Yes, questions can be merged. It may be appropriate for questions 2 & 3. What does everyone else think about that?
Where there are multiple accepted answers, the accepted answer of the merge target remains the accepted answer. Generally speaking, the merge target should be chosen on the merits of the question. Where two questions are of equal quality, the older question should be the target of the merge. Exceptions should be noted in a comment to the question, as should the implications of the merge. This is important in order to not alienate members of the community by futzing with the questions.
Continuing on that topic, care should be taken with decisions to merge questions. I know I feel a strong sense of ownership to my answers (and the few questions I ask). However, we must also keep in mind that the point of SE sites is to have good questions and answers for now and the future. Having useful answers split across multiple questions hinders the goal of having good reference material on these sites.
Along these lines we should not worry too much about losing 15 rep points for accepted answers losing that status due to a merge. Overall, it is a small amount of rep and usually less then the rep from upvotes. A merged question should benefit from increased visibility, though -- of course -- there could be more competition.