I think he sees you giving your attention to others and wants it for himself. Kids' emotions are pretty primitive when they are young.
Along with the others, I think sending him to another daycare sounds like a great idea. He's going to keep testing you if you don't, and you also need (for professional reasons) to not be dealing with this in front of the other parents. He'll probably act fine in a different setting, where he is not constantly faced with Mommy apparently not being attentive to his every whim.
As Lis51 says (and if you read her posts, you will understand), you are not the only one whose 4 year old is driving you nuts. Do take the time and go through some of the other posts, you will see lots of good ideas to help.
But being specific. I've got a feeling that with you running the daycare, you obviously have had to have other children around all the time. You also have had to give them attention. Somewhere along this timeline, your son learned that if he wanted attention from you, he needed to do something to get your attention. Sounds like he has found various ways to do that. Now you need to change this learned behavior.
You do this by being immediate and constant with punishment. Pick only one or two things to work on. Realize that experts say it will take 28 days for the change to happen. Most parents give up after a couple of days and switch to another method and bingo, the child doesn't get the message . And yes, the timeout will work. But it won't happen overnight and needs to be done correctly.
You do have a good idea of him going to another daycare. I think it is worth trying for several reasons beside just your sanity. With you out of the picture, I do think his behavior could change because he is not constantly reminded that you are around. Of course, the first week or so - it could be hell. Do warn the daycare people and do some research on them. But I have seen lots of kindergarten kids just go nuts for the first few days of school, and about 40 min after mom is gone, they are playing. In a few days, all the initial crying has stopped. Hope this helps. Keep in touch.
You are not the only one who is having a hard time.
My mother in law and sister in law are teachers, they have never agreed on being teacher for their own kids. Maybe taking him to another school is not such a bad idea and it will give you time to "take a break" and come back to him with lots more patience in the afternoon.
My son for example is very adjusted to the structured discipline he gets at school.
Since you mention all sorts of punishments I figure the problem is you haven´t been consistent with one method. And it must be very difficult to discipline your child and take care of other children at the same time.
I wonder how things are going at home. I think that when something´s not right children act out this way, in my opinion he´s screaming for attention and maybe for someone to lead the way.
I wish you the best of luck.