The first braking zone with probably cause a few cautions at the start+restarts. The racing line is around the outside of the corner. To overtake in the corner you have to take the lower line, which forces you up the track as it has less grip. Since you go up the track, you'll probably hit the car you're trying to pass. The same applies to the final corner too.
I'd save passing at HSR for the braking into the first hairpin of the esses, or using the draft out of the last corner and down the straight.
The race there shouldn't be wet enough for intermediate tyres, but there is still a chance. The fastest that rain falls in GT5 is 4% per minute, so if we get that for over 10 minutes (something around that) non-stop, you'll probably want inters.
When the sun is out, you cannot see the pit entrance until you're pretty much in it, due to the change in brightness when exiting the tunnel.
Since spinning is more likely in the wet, I'd suggest that more simultaneous single car incidents than in a dry race should be needed for a caution. It's 2 in a dry race, so maybe increase it to 3 if the track surface is 20+% wet.
EDIT: Just had a dry practice session with Leonardo at HSR. His setup needs a little tweaking for the banked corners (he span there more than elsewhere), and he also still has a little bit of lag, though barely any. I also found out the fastest time possible for me and my current setup on low fuel (not that I'm telling
).