I know that OMP make 2 different roll cages,1 for a sunroof fitted car and 1 without.,I dont know about other makes but would imagion they do aswell.When ordering youre cage tell them if you have a sunroof fitted.Also,some cages run tight to the bulkhead and need the dash cut at the ends,others dont,so ask questions before you order to see how the cage runs inside the car.Personnally it wouldnt bother me to cut the end of the dash,but other owners may not want too.I personally dont know if a cage would fit both a S1 and a S2,at a guess I'd be 90% sure it would,but again find out when ordering.
For a wet track you should soften up youre dampers and reduce tyre pressure a little.You will have to experiment with the pressures but around 5 psi less (when cold) would be a good starting point.Hope this info is off value to you,regards Micky