I have twin boys that are nearly two now, but were starting to hit or push or pull hair (mainly to each other, but to my older daughter as well) around 18 months. With my older daughter, and with my twins, I started using time out at around 18 months. Since my daughter was the first, it took a while for her to get the hang of what time out was, but my boys caught on rather quickly because they saw her doing it. So, they go to time out every time they do something mean to someone else (for about a minute or so) and as soon as they come out, they have to go tell the person the were mean to that they're "sorry." (since they weren't talking yet, "sorry" was a hug, and mama saying sorry for him.) So far, this has really been working for me, so I'm not sure what else. Some people recommend repeating the action back to them, but since it's hitting, I don't know if I'd be comfortable with it. When one of my boys pulls hair, I will pull thiers back occasionally. Not to hurt them, but to say "ow. ouch. It hurts when you pull hair" while I'm tugging (gently) on his hair. That way he associates the words "pulling hair" with the action of pulling hair. I'm not sure how I would do that with hitting, but it's worked with pulling hair, pinching, and even biting. Anyway. I'm sure you've heard of time out before, so I don't know if it really helped any. But that's what has worked well for me. I think because part of all my kids' personalities so far has been disliking making me or my husband mad or disappointed with them. They much prefer hugs and praise than getting in trouble, so hugging to say sorry and showing affection after doing something mean is natural to them. Some kids don't care if they get in trouble and time outs may not work as well for them. The key is to find what he responds best to, and do that. (easier said than done, I know). Good luck with it.
As far as the dangerous stuff, I think it just comes with the territory when you raise boys! I never had much trouble with that kind of stuff until I had my boys. It was like night and day between my daughter and the boys. It's annoying as all get out, but the only thing that has worked for me is to get rid of all opportunity for them to do the dangerous stuff. Like with your coffee table, you may just have to move it or put it away until he gets older. For my boys, they started out with a rocking chair, book shelves, lamp (on top of the shelves), books, and other toys in thier rooms when they were first born. We switched them to twin beds on the floor around 15 months (because of a move) and between then and now (just shy of 24 months) their room decor has dwindled down to just the beds (and bedding) on the floor, a night light that we have screwed into the wall out of reach, and a short, wide, two-drawer cabinet with the handles busted off(because they tried to climb on them) solely there to block the outlet that the nightlight is plugged into. Everything else that used to be in the room was either destroyed or became too dangerous. The bookshelves were knocked over trapping one or the other of them underneath twice because they tried to climb on them. The books were either chewed or ripped beyond salvation, the rocking chair was being banged against the wall because they rocked it so hard, and the toys were used as weapons to throw at one another.
So... It may just be that you have to put stuff away until he's old enough to understand that he's not supposed to climb on it or whatever. If you find another solution to that issue, I would be SO glad to hear it! ;) Sorry for the length. Good luck with everything!