The E and F were both produced from 1937 and used in Spain. The Z was already in use by the time of the Polish campaign, and i think was the main 17 is use during the BoB. The P was still is use as a recon aircraft, but i think the older bomber versions were being withdrawn.
The P i have i am doing in markings for the Polish campaign, i'd also like to get their F for a Condor Legion aircraft.
I am surprised RS have not done a 17Z yet, but then most of their kits do seem to be more obscure subjects.