I think every child needs approached differently, so what I suggest is what I would do based on what you wrote, but you know your child and family best. Maybe it will spark ideas for you or permission to try something different.
Yes, I’ve got one of these. If I said black they said white. If I said yes they said no. If they didn’t want to do it they would do anything possible to avoid doing that thing. I have another that is not as extreme in this area but is also more than the rest of my kids. My most extreme is now 10. We’re in a better place relationship-wise. But it was not a quick fix. And it is mostly not the fix you are going to want to hear.
The problem begins with you. Not you, really, but your responses/requirements. My motto for this child became – unless it is a matter of salvation or legal issues (breaking laws) then it is probably not worth battling over. I had to become extremely clear in my own mind about what was worth the struggle I knew would happen when I gave a direct order/assignment.
For example, you mentioned a lot of things you are correcting for during a 5 minute handwriting (where he sits on the cushion, making noise while writing, dropping his pencil, changing his grip, starting writing a letter from a different point than the traditional one you are teaching). Stop. Just don’t say anything about it. Who cares if he is doing it wrong? Right now he wants to write so let him do it. And when he matures and finds a reason to want to write neater or has a personal reason to need to write without making noises then he’ll make that change because he wants to. It’s not a battle worth fighting.
I would be one to drop all academics/handwriting and when he wanted to do some I would say “Great, here is your paper/dry erase board, here are the letters on a page to look at, have at it.” And then I would walk away. If he asked for help I would show and verbalize the way I was writing a letter, then hand the pen/pencil/marker over and walk away to do something else and leave him to it.
Do not fight battles that don’t matter. You will destroy your relationship, but you will also lose all capital for fighting the big battles that really matter. If you are both locking horns over everything then he can’t tell what is really important and what is some silly little thing you both are fighting over, so he will fight as hard over little things as big ones. Save your energy and struggle for what truly matters.
Now, let’s move on to what you DO want to do. You want to set very clear rules for your home that you do enforce. For example, “If you are hungry you can eat what I make for meals, during meal time only.” The corollary to that is if he doesn’t eat during the set meal time (ex: 5pm-6pm) then he’s tough out of luck. You don’t beg him to eat, pester him to eat, order him to eat. You set out his plate at 5pm and you remove it at 6pm. This can apply to EVERY area, but food was an easy one to show.
Academics, for a child who is not 5 (and shouldn’t be having formal academics anyway), fall under obeying the law (we have homeschool laws to fulfill). For us with this particular child it was a 2 part approach. 1. Require only what you must to fulfill the law. 2. Require they do the work before they ______ (eat lunch, go outside, go to lessons, watch a movie, play with their toys, whatever they do….). If during the course of not doing their work they miss their meal, oh well. Sympathy for being hungry is always allowed, but you remind them that they missed that opportunity because they had not done their school work yet (which you must be sure is totally doable for them if not too easy when you are first fighting this battle). Don’t fight. Don’t argue. Don’t nitpick over every little thing. Only fight the big battles that matter.
You may consider Parenting with Love and Logic, they run a lot along these lines, if you are looking for reading for you. But I don’t like everything they have, so find what works for you.