Well, Churchill III, IV, V and VI all had riveted hulls. Starting with the VII they went to welded. I assume that is enough of a change to mean you can either do the riveted hull variants, or the welded hull variants, but that would be two separate kits.
Churchill I and II looked significantly different from the models that followed. Tracks were not fully covered, and the turret was smaller.
Starting with the III the turret size and shape changed significantly.
Starting with VII, the turret size and shape changed again
So just based on this, I could see possibly three kits:
Mk I and II (2 pdr armament) - Saw little front-line service. Dieppe comes to mind.
(@ 1,350 produced)
Mk II, IV, V and VI (6 pdr and infantry support howitzer) - Main versions of the Churchill, saw service in Africa, Italy, Russia and Normandy
(@ 2,750 produced)
Mk VII and VIII (QF 75) - Known as the Heavy Churchill (2 tons heavier). Late-war version, saw action in Normandy and Italy
(@ 1,600 produced)
So the second option looks to me to be the best bet for a multi-version kit that will have different turrets/weapon, and greater fielding opportunities.