First off, the "terrible twos" start at about 18 months and last until about 2 1/2.
Second, the primary reason your are going insane is that you are trying to do so many things at once. Surviving a toddler is not bad unless you try to get something else done (like taking care of other kids).
He is acting up for a few reasons. He is exploring his world to see how things work. He is testing the limits so he can get a feel for how far you will let him take it. He is punishing you for ignoring him, and he is begging for your attention.
The key to getting out of this behavior is to be consistent and to pay attention to which of those reasons he is misbehaving. If he is just exploring, then make your house a place he can explore without getting into trouble at every turn. Put things he can't touch away, put gates where he can't go, and child proof everything. If he is testing your limits, then show him where the line is. Allow him to immediately test it again, and show him the line again. After about the third time in row that you dicipline him, he will get the point and move on. If he is upset that you are paying attention to something or someone else instead of him, then give him a cuddle and a kiss and something really exciting to do while he waits for you. Try not to discipline him too hard when he is just asking for your attention because it will just backfire. Don't allow the behavior either, but sometimes the best response to him hauling off and hitting you is to get down to his level, give him a love, and say "I know you want mommy to play with you, but I have to feed Jane first.. then we can play trucks. How about you go get all your trucks and line them up right here for us."
Also, whenever you talk to him, get down on his level, face to face, hold him facing you, and speak clearly and calmly. My 20 month old turned from nightmare to very obedient the day I started getting off my butt and walking to him to speak to his face. That was all it took.
The baby stage is so hard because you aren't getting any sleep and you feel like if you hear one more minute of crying you'll go insane. You can't wait for your baby to grow to be a toddler. The toddler stage is so hard because they test everything, they get into everything, and they have unlimited mobility with unlimited energy. You can't wait for them to be preschoolers and calm down and understand the rules. The preschool years are so hard because everything is "why", and "how", and you have to explain everything from the color of water to the most complex theology lesson. You can't wait for them to start school, learn more, and ask easier questions. The school years are so hard because the kids are learning nothing from you anymore and everything from the kids at school. They suddenly have attetudes and words you never thought you'd hear in your house. Next thing you know, they're teenagers and you can't understand why you were in such a big hurry to get here. You just wish you could hold a baby that loves you and can't talk back. You'd take crying/testing/asking any day of the week.
Take time to yourself every day, don't feel guilty for making your husband take over for 15 minutes when he gets home while you "run away". Be as relaxed as you can be so you can enjoy everything that your son is. Experiment with whether it is easier to take care of him at home, at the park, at a friend's house, etc. My kids are so much easier to handle when we go out.