I didn't ready the other responses, so I hope this isn't redundant. I think the MWF program you enrolled him in will be perfect for both of you. Here's my 2 cents...
I run an in home daycare and have 2 school aged kids of my own. I really believe that at least 1 year of preschool is really beneficial for kids before they go into kindergarten. Some people don't like daycare (which is fine) but I see daycare as a good stepping stone to preschool and preschool a good steppingstone to kinder. Both help children learn to trust and take direction from an adult other than mom and Dad and helps the become more flexible in both dealing with different environments and different people (both kids and teachers).
In most cases preschool is not about academics. It's really about social skills. And in a good preschool, kids get a different experience that will benefit them more than a Mom's group (short timeframe, same small group of kids, Mom's constant supervision) or a park and rec class that is structured.
I don't currently offer a preschool "curriculum" in may daycare, but we do lots of preschool readiness types of things. Learning colors, shapes, ABC's, counting, social skills (sharing, using words to express feelings and needs, table manners), painting (both easel and table, fingerpainting, brush painting, and with different mediums), cutting with scissors, gluing, playdoh, small and large motor skill play, art music, sign language, growing plants, the growth cycle of a butterfly etc... BUT even with all of that, I have a wide range of kids (from 6mo-5 years). It is not the same for the preschool age kids to do all of those things at my house as it is to do them with KIDS THEIR OWN AGE. That's the big difference.
Depending on your son's personality, he might be fine without preschool. But I would say in most cases, kids who have at least one year before kindergarten have an easier time than those who don't.
Good luck!
I also wanted to add that I didn't send my kids to preschool until they were 4. Most of the kids I see in my daycare are ready for more socialization by the time they are 3 or 3 1/2. This is not true of every child though.
It sounds like you already found a preschool that you like, so that's great. I always tell people to keep in mind that there are lots of options with preschool, just like in daycare. You want to look at a lot of them to find the one that is right for you, and stay aware and involved that your child is getting what he needs there.