Oh my stars, you are doing fabulous!
I wasn't doing that much when my older boys were 3.5yo (they're now 7yo and 4.5yo). Just this July I started using an actual curriculum for me and the 7yo because we/I needed that kind of structure right now (PPD, was alone with 4 kids until my hubby quit his job, house on the market, etc. - so I get at least part of what you're going through).
There were days where the kids were lucky if I got out of bed long enough to get them hot food and I didn't sob for 30min-2hrs. Many, many, many days involved them eating cereal and turkey sandwiches and PBJ and yogurt (things they could get themselves), and I'd 'parent' from the bed upstairs while nursing the babe and getting up here and there to change diapers and put the 2yo down for a nap and such.
Only things I could add are definitely
take up the family on watching your boy.
Having some time to yourself is good, even if it's sobbing or taking a nap in bed or taking a bubble bath or reading the trashy magazines at the bookstore - you need time to recharge yourself.
Bonus if you have some local friends there you can hang out with and just gab. Even if it's a playdate and all the kids are messing around in the yard and the moms are sitting inside watching through the window - it's *so* nice to have adult connection during the day (and the kids get to play unfettered, so cute with decently behaved children!). There's only so many conversations about legos and dinosaurs and why you cannot wear just socks and underwear to the grocery store today before you start to feel your own brain oozing out.
When I was actually pricing out mental institutions for myself, we broke down and started paying a friend (she does in-home daycare) to watch the older three for me to get a break. It wasn't exactly daycare/preschool and it was at our own pace with our own schedules, so maybe that could be a different option for you as well? My friend also homeschools, so at the time she had a 10yo boy at home that my 7yo adored, and she knew where I was coming from homeschooling-wise so to speak.
And then meals. This is a thorn in my side right now since we all have to eat, and it's all on me - whether I have to prep it myself or just make sure I've got all necessary items in the kitchen/pantry. Any way you or your dh can plan ahead with that? Like do a weekly (or bi-weekly or monthly) meal plan, have all the ingredients on hand for that week or two, prep everything on a weekend so it's either in the fridge or freezer ready to go? That alone can make things seem so much smoother, you know?