My dh works fairly long hours as well. He leaves the house around 6:45 and isn't home til 6 pm usually. He often has evening dinners/client events as well, so a fair amount of the time he doesn't see the kids til the next day. He also needs me to accompany him to some of those, which further busies our schedule.
My children are 7.5, 6, 4 and 17 months. We have always homeschooled, but my two older girls did MDO one day a week when they were toddlers and I was expecting our third dd and it was helpful at that time as I had no other way to go to my appts, have a bit of a break, run a couple errands.
We have loved homeschooling and I'd probably recommend it in your situation. I agree that *probably* the K schedule would be even harder than spending an hour a day doing K with your son (that's about all it takes!). That being said, if you are overwhelmed, your health (mental or physical) is suffering as a result or your marriage is suffering, I would find some type of help. That might be MDO/preschool for your youngers, a mothers' helper or babysitter on a regular basis for you to take care of yourself, house cleaning help (I have had this since my 3rd child was born, once a week) or even putting your oldest in school if you thought that was the best solution. If you have family who would help regularly, even better, but I know most people don't have that (we don't!).
My dh reads to the children most evenings and is a wonderful father, but he is not home to do the hands-on homeschooling most of the time. I began to feel burned out this winter and we will be using a university model school next year. I didn't do it in K for my oldest b/c it just wasn't worth it to me to drive her to school (its just two days/week), have to be on the school schedule and lose the flexibility of full time hs and still have 3 littles at home to care for and then have to pick her up again. Full time homeschool was the best option *at that time* for our family. We have loved it. My children are very very close and they have been able to learn at their own developmental pace, which I think is especially critical in the early years.
I have actually been more overwhelmed this year trying to manage 1st, K, a 3 yo and a baby and meeting the needs of a very busy husband and household. The UMS near us is *so similar* to what we have been doing and want to do that it is a great fit for our family and we will still have the flexibility a few days a week and time all together that we love. The biggest draw for me this year was that my 3 older girls can all attend 2 days/week. To top it off, the church where the school meets also has an MDO program (the one where my dds went) that overlaps by one day. So I will have one day where they are all there and I only have to drive to one place. It wouldn't be worth it to me to drive all over town or only have one child at a school. And I wouldn't want them gone more than the two days. That is plenty for me.
Try to think of your educational choices on a year-by-year basis. I used to think we'd never do anything but full time school forever, but I am learning to take it year by year and seek out the best choice for our family each year.
The other thing that helps us is to schedule picking up time around 4:30 each day. I also tend to bathe the children right after that so the house is relatively neat, children are clean, calmer after the bath and in pjs and we are ready to eat when dh arrives home. If he is going to arrive after 6 pm or if we are just having a severe meltdown day, then I feed the children their "nursery tea" around 5 and they have reading time, Bible time and tuck ins with Daddy when he arrives. I love the ideal of the family dinner (we still do it several nights a week at least), but some days you just have to settle for calm fed children, calmer mommy and less chaos when dh arrives home. A good read on family life (whatever school option you choose) is For the Familys Sake by Susan Schaeffer Macaulay. She is a Christian though, just fyi.