OK try not to be so hard on yourself. Having children exposes us and tests us in a way that nothing else does and we all struggle with it in one way or another. You obviously love your son very much, you just feel overwhelmed a lot of the time and just need a practical way of dealing with it.
The first thing that struck me was that you describe your four year old using quite adult language such as "know-all" and "control freak" - labels that are not really appropriate when describing a very young child. This suggests that you need to adapt the way you view his behaviour as you're not seeing things from his four-year-old viewpoint.
At this age, he is not deliberately winding you up all the time. There will be reasons why he does the things he does. You don't mention any specific things that wind you up but at this age he will probably find repeating rituals comforting, he will probably get frustrated if he wants to do something all by himself and can't, he may not feel able to walk away from you when he gets upset because even when you're cross you're still his comfort, he may truly not understand why his actions aren't helpful or appropriate in some situations etc. etc.
All these things can lead to unnecessary tensions if the parent misinterprets the intention of the child. When your child's behaviour irritates you - try asking him why he's doing it first. You may find that in his world there is a "logical" reason for him behaving in a certain way that isn't to do with winding you up. Try asking yourself - is he being naughty or is it just his behaviour irritating you? If he's irritating you and you're over-reacting, ask yourself is it him you're really angry at or is it something else - your partner say, or are you subconsciously recreating your own parents' behaviour? You may be reacting emotionally to behaviour rather than constructively and only you can understand why you might be doing this.
I think you do understand the dangers of crossing the line into emotional abuse such as making damaging personal remarks e.g. "I wish you'd never been born" and making a child feel permanently afraid of how you are going to respond to them. This kind of thing can affect a child's emotional development and I know you don't want to do this to him. You are his role model - his is learning from you about how to deal with and express anger.
So make a note of the things that trigger your anger and recognise the early signs of your own anger so that you can self-diffuse without losing control and anticipate potential situations and think creatively about how you can avoid them escalating into shouting.
If you can't walk away then try imagining you're talking to another adult, or imagine him as a baby or even imagine that someone you know is watching you. These things might just pull you up in the heat of the moment. Maybe even record yourself or just your voice and play it back to yourself later and it may just give you a shock factor that has a lasting effect. If you imagine another adult shouting at you and imagine them twice the size, you can get a feel of how you're coming across to him and how scared he might feel. Find a phrase that works e.g. "I'm the adult" or "I'm a good mum" or "I love my baby" and say it out loud to yourself when you feel the anger rising. It might just snap you back into focus. Delegate to your husband if he's around and watch how he deals with difficult situations. There's no reason why you should be dealing with everything.
Finally think about how things are for your son - does he just hear constant negativity - "no" and "don't do that" or "hurry up!" etc. etc. If so, set yourself a personal target to say four positive things to him a day - tell him "well done" if he does something himself or gets something right, show an interest in him - ask questions about his favourite things or just take him somewhere a bit different to stimulate a different kind of vibe. Have fun with him and learn how to enjoy each other's company.
You've done the hardest thing in admitting your struggle. I've no doubt that you will be able to manage your anger and hopefully the articles I've attached will be of some use. Take care and all the best x