B.S.
My two little girls are 23 months apart, and I really have to say, there has been amazingly little friction. Now they are 39 mos and 17 mos, and they appear to be the best of friends. There is the occasional toy-snatching, but other than that, they really seem to enjoy each other - the first thing they do when waking up is to go look for sister.
I followed my pediatrician's advice, which was to give the older one some space on the regressing issue. We were totally off the bottle, but she wanted to do all the things the baby did, so there was a brief pacifier renaissance, and we're still doing the bottles. Sigh. But not that often. And once the little one's done with them, I think they'll be gone for good. The older one still likes to pretend to be the baby, wants me to cradle her like a baby occasionally and even provides little realistic "waaa-hh's" for the maximum desired effect. Occasionally likes to sit in the high chair, and took a couple of naps in the baby's crib.
I let her touch the baby whenever she wanted - didn't encourage or discourage, but Susannah is a pretty gentle kid. I'd play that by ear, depending on your older son's disposition.
But for the most part, I just tried to avoid distinctions like "oh, that's only for the baby..", etc. That's kind of divisive and tends to make the older kid jealous. There was even a period where Susannah, who is pretty big for her age, would climb up into the baby swing...which held, thank goodness.. If I had to discourage her off of something, I'd say "oh, that's gotten too little for you, what a shame, oh, mannnn!!", rather than telling her that's only for the baby.
Whatever issues we had, I tried to look at it from the older kid's perspective (b/c frankly the little one has no idea of what's going on anyway...) and react with her feelings in mind. Daddy did a lot of putting the little one to sleep while I preserved the big one's sacred bedtime routine. And once the little one arrived, Daddy ramped up his one-on-one activities w/ the older one big-time. The week we came home from the hospital, he took her on trips and activities nonstop and she just loved all that special attention from Daddy. (I also made sure I took her to the playground just the two of us that week, too - she thought she'd hit the jackpot!! At least it put some of the new awkwardness/stress in the background and she was exhausted every night..
There was a brief regression on the sleeping the first couple of weeks, too, I hear that's pretty common - I made sure to respond as quickly as I could, given that the little one was waking me up, too. One night my husband was delighted to race down to her bedroom (because it was the first time she had screamed for "Daddy" when she was frightened..made him feel like such a hero!) But she resumed her sleeping-all-night schedule after only a few times..
Right now everything is going great w/ the relationship between my two girls, I'm really very impressed. Now that the little one is so very mobile, she occasionally hurts her big sister unintentionally. I make a big show of telling the little one "That's not okay, Katie, you hurt Susannah, you should say you're sorry.. Say sorry, Katie..." and the older one will look at me in amazement and say, "But Mommy, Katie doesn't talk yet. She can't say sorry!" It's funny, I know, but it does help boost Susannah's sense of fair play and that I know the baby's not always the innocent or injured party.
And I've had a couple talks with Susannah about her feelings about the baby, to help validate what she's feeling. Like "That baby is always crying. That's really annoying, isn't it, when Mommy has to help Katie when you want Mommy to read you a story?" or "Katie broke your toy. I'll bet that made you feel sad about your toy and angry with her, huh?" Most of the time just knowing that I understand how she feels has helped her move on without taking it out on her little sister.
My favorite parenting book, which addresses some sibling issues too, is "Between Parent and Child" by Dr. Haim Ginott. It was originally published in the 60's, and the good doctor is long dead, but I love his approach and find it almost universally useful with my kids.
Good luck! I had a major guilt meltdown when I had my second, but seeing them so happy together makes me convinced that having them so close was the best thing that we could've done.