Wow. I can't believe how many people think you should hit a baby (he's not even 2 yet; he's still a baby in my eyes) especially when you said you don't do corporal punishment. Here's what I would suggest. Figure out what his hitting triggers are and redirect him.
If he's hitting because he's angry, tell him you can see he is mad, but we don't hit people. Tell him how to deal with his anger. Stomp his feet, hit a pillow, clap his hands, etc.
If he's hitting out of frustration, tell him how to ask (or sign if he's not too verbal) for help.
If he's hitting because he gets excited, I would redirect and ignore it as much as possible so you don't make a big deal about it.
If he's hitting for attention, you can approach it from several ways. If you can tell he's getting ready to hit, immediately distract him like suggesting you read a book or play with legos. Catch his hands and redirect him to a high five or a game of patty cake. Or firmly grab his hands before he can hit you and tell him, "I don't like to be hit. Hitting hurts. I like hugs." Or you can tell him, "I don't like to be hit. Hitting hurts." And then put him down and walk away for a minute. I used a lot of these approaches with my daughter when she went through a short hitting phase without resorting to spanking her, hitting her back, or even using time outs. And she wasn't what you'd call an easy going child. Since you said he's hitting you and then kissing you right afterwards, it sounds like he's really enjoying the cause (hitting you gets a response) and effect (if I kiss her right after I hit, then Mom's happy). I'd probably redirect and ignore as much as possible.
You might want to make a big deal of all the things hands are for like: clapping, high fives, turning pages in a book, feeding ourselves food, etc. There's even a book out there called "Hands Are Not For Hitting" which you might find useful to read with him.
I definitely wouldn't leave him alone with the baby. And you might to prepare him as much as you can for the baby. Tell him what having a baby around will be like (crying, nursing, getting diapers changed, needing mommy a lot, etc). There's going to be jealousy of some degree no matter what as he gets used to a new sibling. So you might want to point out all the things HE gets to do that the baby can't (drink from a cup, use a fork, jump up and down, ride a bike, etc.) I like this approach better than telling him he's a big boy over and over because he probably likes being the baby and it will make regressions to baby like behavior (like insisting you carry him) worse. Tell him what being a big brother means. When the baby comes, include him as much as possible with getting you diapers, picking out outfits or blankets for the baby (even now my daughter will pick out and bring me clothes for my 1 year old). Praise him for being a good big brother. I had people greet my daughter before meeting the baby too.
Congratulations on your new baby and try to enjoy the time you have left as a mom of one. Have compassion for him because if you think you might be a little sad having to be shared (and I know I did), imagine how hard it is for him.