since it is done, 001 would be rarest (at this point, barring any more limited, finite ref. in the future.
In terms of actual production UP TO THE TIME YOU POSTED THIS QUESTION, I believe the 004 is the rarest (not including the Ph. Starck piece unique) - even fewer than the 008.
And about the 001 no. 18 being the first 002 - this shouldn't be possible, as the 001 and 002 were different movements; the 002 started with the mode pusher; the 001 used a more "traditional" crown position technique.
Are you sure the 001 numbers 17, and not 18? 18 was mentioned to me by both RM USA and a (admittedly off the cuff) conversation with RM himself.
Cheers,
TM