My ds2 is 4 1/2 too and we are literally just coming out the other side of this, just as I was beginning to give up all hope.
We are now at the stage where 99% of the time ds will walk away and tell an adult if someone has hurt him/taken a toy/been mean rather than just smacking them across the head. He now 99% of the time will say "I'm very angry now, I'm going to rest in my room" he will now 99% of the time use his words instead of automatically lashing out.
It was hard work and I wondered if we would ever get there but we did and you will too. Choose a discipline method and stick with it. When you get to the point you think it's not working, keep at it for another month. Positive parenting works with my ds1. It absolutely does not with ds2. We went down the 1, 2, 3 magic route with a few tweaks to suit us.
I agree that he sounds overwhelmed and overstimulated. He does so much in a week and he needs time to just be.
My ds2 goes to Kindy. On Kindy days (he finishes at 2.30pm) we come home for a snack and a rest and some quiet activities.
On non kindy days, we do all of our activites in the morning. Park, beach, swimming, soft play, bike rides etc a picnic out in summer and the afternoons are back at home doing arts and crafts, lego, gardening, whatever he wants to do.
I don't take him to any other organised activities like football or swimming lessons anymore because what he's doing now is enough and we've finally found a good balance. We'll try more structured activities when he is older.
Good Luck.