which model should I choose for shooting a doc?
The a57 has a DSLR form factor, an EVF viewfinder, good auto-focus, good low light performance, 24P, 30P and 60P, an APS-C sensor, plus a low price, it may be just what you are looking for.
BTW the camera has face recognition and does a good job of follow focus as your subject walks around a room. Check-out this video shot with an a57, notice that they are using the camera EVF http://vimeo.com/40573835
Here's one I shot with a NEX 5n set on Program, http://vimeo.com/29216506 same sensor as the a57.