If you're not familiar with DIXF, you should look at Data import/export framework user guide (AX 2012). It will answser some of your questions, such as whether it's a part of AX (it is).
Regarding 1), I'm not sure how you distinguish between migration and replication.
Regarding 2), I though you would simply set recurrence inside AX, without any custom development. There some services and you can expose anything you like, if you have a good reason for doing it. But then you may want to use document services instead of DIXF.
Regarding 4, transformation options are limited, but the fact that one entity consists of several different tables is not a problem at all; it's the usual case and the reason why we have such entities in the first place. If you need some complicated transformation, using AIF may be easier (see About the AIF Pipeline and Transforms), although exporting data through DIXF and then handling transformations separately may be better from the performance perspective.
