I don't race anymore, but did cross when I did. I would say keep it at 30 for CAT 4. Beginners need somewhere to start and cross can be intimidating at best.

My question is why does he have a 3-4 race and a 1/2/3 race? Why not a 4 race and a 123; or a 3/4 race and a 1/2 race.

Seems weird to me, but I never really raced cross in an area where there were a lot of women competitors so it was usually just open here.