Does the Church have a preschool? The place where you go for Bible class?
And I assume he is potty trained already and able to read? If he goes to those things 4 times a week... then, don't feel you "have to" have something structured for him on his off-days, at home. Kids... really need just play time too, just hanging out, playing on their own. That is how they learn too. Kids can become over-scheduled... and at this young age, it is not imperative that they have structured things everyday... nor extra-curricular classes etc. Kids, need days-off too.
Next, go according to his readiness. I have heard, that with boys, they sometimes benefit from starting preschool later...
I have a 3.5 year old boy, I am contemplating the same thing. But, ultimately I will go according to my son's readiness and "want" for school. Right now, he does NOT want to go to school... even though he has been to school with me and his older sister... where I do volunteering at her school. So he does know about school... and he even has friends at my daughter's school. Yet, he says he does NOT want to go to school yet.. .and he wants to stay home. He is also still not 100% on the money with pottying. My daughter on the other hand, ASKED to go to school, at this same age. Begged us almost to start school. So we enrolled her.
all the best,
Susan