I am re-reading this a few years later and just wanted to add a few notes that might help others in a similar situation.
• I did some reading on Oppositional Defiance Disorder (ODD) because I felt like his behavior was inching towards that diagnosis. I also found some information that gifted boys can often get misdiagnosed as having ODD, and there can be some overlapping traits between ODD and being gifted. The treatment for ODD is often coaching the parents on how to react to their child and teaching parents to coach their child through emotions. I found the book "10 Days to a Less Defiant Child" quite helpful. The number one trigger for my child is to take something away as punishment. Whenever possible, we try to have him earn privileges through good behaviors rather than taking things away.
• My son finds his same age peers very irritating. Now that I have some perspective - being touched by other kids without his consent all day long was probably sensory overload. It was the worst in preschool - he was very verbal and the other kids just weren't able to respond to him and just sort of stare at him and get nervous, they also constantly violated his personal space - bumping, smashing, the preschool classrooms I visited didn't give children any personal space. In kindergarten, kids had seats at shared tables and shared supplies, carpet/circle time... but there started to be some rules about keeping hands to yourself, but I'm sure there is still tons of touching, bumping. Now that he's in 2nd grade, he has a desk to himself and a box of his own supplies. There are/were covid restrictions that gave him more personal space. What a relief. He still occassionally pokes, trips, irrritates kids around him. But, it's not constant and he has more control.
• Any kind of self-serve intellectual stimulation is a super helpful coping device and it's been worth my effort to encourage and support. At home he has access to a bunch of stuff - audiobooks, books, writing and drawing materials, building toys, etc. He uses this stuff constantly. When he got to school, he was cut off from all of this. In KG, the teacher didn't allow building blocks or reading books when you are an early finisher on your assignments (too distracting to the rest of the class). Now, in 2nd grade both the teacher and my son have made better accommodations - he always has a chapter book to read at his desk, he draws on the back of his sheets if he finishes early, my son is very mathy and makes up challenges for himself - how many minutes until recess? How many hours until the weekend? If there's X amount of calories in a serving of milk, how many calories is the whole container?. He's currently playing baseball, but gets bored and becomes distracting when there's no action - I'm trying to encourage him to keep track of the outs and/or runs. I play verbal games with him when we're waiting for the doctor or are in the car for a long time. Any sort of fall back, self-serve thing that can be done to keep his brain busy is helpful for everyone, and he's learning to do this for himself.