I would highly recommend finding yourself a good Occupational Therapist who has lots of experience working with special needs kids. I'd recommend having him evaluated for sensory integration disorder. It is very common in kids with special needs. My 6 year old has autism and sensory integration disorder. It is very common in kids with autism and in other kids as well. Sensory integration disorder is basically where a kid doesn't perceive sensory input in the way the rest of us do. Some kids are sensory avoiders, some are sensory seekers, and some (like my son) are mixed - they do some avoiding and some seeking . To me, what you are describing sounds like a sensory seeking behavior. A good occupational therapist can help you figure out what is reinforcing the behavior (why he does it, what he's getting out of it) and then help you find a way to extinguish the behavior. Since your child is over 3 and has special needs, is he involved in the school district early childhood program? If he is, you may be able to consult with their occupational therapist. Some schools also have a behavior team that can be helpful. If you aren't involved with the school district, I'd highly recommend you contact them and see if you can get involved. They have great programs for kids with special needs from age 3 and higher...
As far as fighting with your husband, that is pretty normal. Most normal marriages end in divorce. When you throw a special needs child and the stress that comes with that into the mix, it just makes everything so much more complicated. You really have to make a special effort to get on the same page and try to stay there. If you don't, eventually you'll split up and things tend to just get more complicated. What I'd recommend is figuring out 2-3 things that your son does that really drives you nuts. Sit down with your husband and develop a plan on how you want to handle it. Write it down, post it on the wall. If everyone is on board and being consistent, whatever you try tends to work better. Whatever plan you develop, stick with it for at least 2 weeks before deciding what you are doing is not working. If you can both agree on a plan, that is cool. If you can't, negotiate that you'll try one of your ideas first and if that doesn't work, then you'll try the other parent's plan. Once you guys learn to communicate, figure out that you are in this together and quit blaming each other for your son's behavior, it will get easier. It has taken my husband and I six years to work together instead of blame each other. We are certainly not perfect but we are in a way better place than we were 3 years ago. And seek professional help. Behavior modification is a science and an art. It is very, very helpful to bring in a professional when you first start. Special needs kids don't necessarily respond to things the way typically developing kids do. Things like slapping your son's hand can be very ineffective because 1. he may not understand cause and effect - if I hit the window, mom will slap my hand. If he doesn't get the connection, all he understands is that you are hitting him and has no idea why and that does absolutely nothing to change behavior... 2. Special needs kids really tend not to get the "do as I say, not as I do" thing. So hitting them typically just results in them hitting other people. If you model that we deal with frustration by hitting, that is exactly what they'll do.
Basic behavior modification is that every behavior has a trigger or a reinforcer (or both). If you can eliminate the trigger, great. But real life often doesn't work like that. For example, my son at 3 would scream like a banshee every time I put him in his car seat and fight me like crazy. I couldn't exactly quit putting him in his car seat so I had to figure out how to quit reinforcing his screaming and fighting (which basically meant putting him in his seat and buckling him in with no negotiating, no stalling, no extra attention - each time and every time). Even discipling your child is attention - negative attention can reinforce behavior just like positive attention can. Once I took my emotional response and my anger out of the situation and just approached it as a matter of fact - "it is time to go, you need to get in your car seat. Do you want to get in by yourself or do you want mommy to help you?" - and then matched actions with words, his behavior got better - once he realized no matter how hard he fought, he would still be getting in his seat, he quit fighting. I wasn't mean about it, it is just one of those things that must be done. It isn't always an immediate fix, but the goal is to fix behavior long term. Not necessarily beat your child into submission right now.
Does that make sense? Again, it would probably be a very good thing for you to see out an Occupational Therapist or even a behavior therapist. Parenting a child with special needs means you need more tools in your parenting toolbox than other parents. Professional help can go a long way towards filling that toolbox with things that work for your child. You'll get lots of "helpful" advice from friends, family members and even total strangers but unless they've raised a child with special needs, chances are their advice is going to be totally useless to you. If the "normal" stuff worked, you wouldn't be here asking for help...
Good luck,
T.