1) On the final watch, will the hour, minute and second hands be "white white" or "white metal" as in white gold or steel? They look like white metal on the prototype.
White metal hands as it is conventional at LUC to match the case metal colour.
2) There is talk of Superluminova but is any part of the watch luminous on the final version?
None: for reasons mentioned in a sub-thread to this posting.
3) Diameter of rear sapphire crystal of display back?
The case is 42mm diameter and as there is an "arena" back or amphitheatre style, the maximum crystal diameter is a little smaller (minus bezel width).
4) With the movement mods, does the PuristS edition retain the flyback function?
Yes. The movement is the same base L.U.C 03.07-L with Geneva Seal and COSC with flyback function. The pusher feel is smooth with distinct but discrete 'break' on start, stop, flyback and reset.