For your last question; I don't think shooting 4x3 is the best option, but then again I don't know what you are printing back onto? Super 16mm, 35mm?
Not many film recorders that go to 16mm neg anyway...
First of all, if you are shooting 24P or 60i, as long as your shutter speed is not longer in exposure time than the capture speed allows (i.e. no shutter at all, 1/24th at 24P or 1/60th at 60i) then there will be no affect on quality or the ability to film-out (in fact, there's no reason any shutter speed would affect the ability to film something out.) If you had a camera that allowed you to select an exposure time longer than would seem possible -- for example, if you are taking 24 pictures a second, how could a per frame exposure time be longer than 1/24th of a second, like 1/12th of a second? It can't. The camera is somehow reducing the capture rate to allow longer exposure times. So an interlaced-scan camera that allows 1/12, 1/4, etc. may be compromising on vertical resolution to give you those long exposure times.
So at 24P, anywhere from no shutter (1/24) to 1/48, 1/50, 1/60, 1/2000, whatever, has no afffect on anything but motion blur per frame. Now a film camera running at 24 fps with a 180 degree shutter would be an exposure time of 1/48, so selecting 1/48 in the DVX100 would be the closest in look to that; however, 1/50th and even 1/60th is close enough that it's not going to make a major difference in look (24P at 1/60 would be the same as shooting in film at 24 fps with a 144 degree shutter angle.) 1/24 would be rather smeary in faster movement and produce a look not typical for a 24 fps film camera. But in super low-light conditions, it may be a good compromise in order to get more exposure, especially if there isn't much movement in the frame. But normally you'd try and shoot near 1/48 at 24P.
35mm print projection is almost entirely widescreen, either 1.85 'flat' or 2.39 'scope'. 4x3 is 1.33. While you could transfer your 4x3 image inside a black windowbox inside the 1.85 projection area, you'd see black borders on the left & right side of the screen unless the curtains can be moved in.
Most commonly, 4x3 video is transferred to 35mm 1.37 Academy, which is then cropped during projection top & bottom to 1.85 : 1, so the best thing would be to compose 4x3 for cropping to 1.85 (or to 16x9, which is 1.78 and very close to 1.85.) Or shoot 16x9 with an anamorphic adaptor.