Oh my, 2 reccommendations for "To Train up a Child" (or, as I like to call it, "To Beat up a Child") in one thread...that's a book I certainly would not reccommend! One person reccommending the book bases part of her reccommendation on that she has "only" spanked her 2 year old 10 times. I guess for most households that's pretty good...but I've got 4 kids, and between all 4 of them I probably have not spanked 10 times. And yet I'm still regularly complimented on their behavior and compassion towards others. I'd much more strongly reccommend "Raising Great Kids" by Henry Cloud and John Townsend or "Making Kids Mind Without Loosing Yours" by Kevin Leman.
It sounds to me like the consequences that are being used for your son's misbehavior aren't really very related to the behavior, and thus could lack effectiveness. Can your son even read? If not, I don't see how writing sentences is helpful. My kindergarten son can read, but neither of my daughters could when they were in kindergarten. Even if he can read though...not really related.
When we've had problems with our boys not sitting still in their chairs, we take the chairs away and make them stand. There was actually one study done where children were allowed to decide to sit in their desk chair in school or stand at their desk, and most of the boys chose to stand and their grades improved when they were allowed to stand.
When he treats a toy incorrectly--whether he hurts someone or not, or whether it is "in anger" or not, it should be taken away from him IMMEDIATELY with a brief explaination "I can see that you aren't able to play with that today. Swinging that toy around like that could hit someone and hurt them." It will only be through consistent reinforcement that your son will learn. If he is allowed to spin in circles while holding a toy at arms length and you don't say anything about it until he hits someone with the toy, what you have taught him is that it is okay to spin in circles with a toy--just don't hit anyone. So he will judge--in his immature 5 year old mind--that he is able to be "careful" and not hit anyone...even when there are other kids 3 feet away from him.
Here are some websites that I thought you might find interesting: http://www.chewymom.com/?p=1074 (about parenting and instant gratification) http://www.kjsl.com/~lindav/notrain.htm (about "To Train Up a Child")