HUGS! Try and stop worrying, no matter how much you plan, read up or get advice on, each second baby is different, it could be worse then someone else or better. The best thing you can do is realize what a great mom you are to your first and the second one is a blessing and you are wiser and more confident now then you were with your first!
I was 40 when I got had my second, so I was worried about the energy factor, my daughter was 3 at the time he came along. I just did it, it was actually way easier, I wasn't such a nervous wreck about all the little things, I wasn't so used to sleeping all night that I didn't adapt to getting up every three hours for those first six months. I think I felt less sleep deprived with my second then I did my first. I think my body adjusted better the second pregnancy.
It all came so much easier! My daughter was old enough not to be in baby mode and not need my undivided attention so much and was so eager to help with the baby. It was a pain as she regressed with the potty training and I had two in diapers but that wasn't for long. Nothing is impossible and you can put your baby on a schedule. The main thing is get him/her used to noise, lay a bassinett in the living room so he can nap on and off amongst the noise as that is the best gift you can give them. Have our son look at his own baby pictures when you are further along in your preganancy letting him know he was that little and all the things you had to so for him, include him in everything, even OBGYN appts.
If he is closer to three he will not be so dependent on you either and got some good "only child" time in. Don't worry he will adjust as long as you really include him in it all.
My daughter would yell at me if her brother cried and I didn't rush to him.
I kept my son in a bassinett in the living room a lot during the day so he got used to the noise and could sleep better. My daughter napped for six months more when he was a baby so that helped putting them both down in the afternoon. One nap a day when he was an infant I put him upstairs in a quieter crib, then as he got older I would put him in his crib upstairs to nap. I just wanted him used to noise so my daughter didn't have to be so quiet.. Then as he got older when he would nap twice and my daughter was up he did great. She was in preschool at 4 when he was one so while she was in school I would lay him down.
I made sure she had gymnastics classes, preschool and her "own" thing for herself too. I explained right off the bat why babies cry, why I have to get to him if he is crying because he cannot tell me what he needs, why they eat so much and all of that. She was okay with it. It was actually harder for her when he was just walking as I had to have eagle eyes and would have to interupt her to get him if he was into something or whatever, he was a climber and I had to micro manage him and that is when my daughter kind of resented the attention I gave him.
Stay on what routine you have now, waking, feeding, changing, a little play and nap for those first three months is all they really need. Then as he/she gets more predictable figure out what works for you. If your son is still napping try the afternoon to lay them down seperately but at the same time to give yourself a break, YOU NAP TOO if you need to! I let myself nap and relax more with the second too, I gave myself permission to not rush to do the dishes any chance I got to just rest too! :)
Hugs and good luck, keep us posted.
I am 44 now, have a wonderful and loving four year old son and a very sweet and caring 7 year old, still don't feel old yet and the sleep disruptions still happen if someone is sick, bad dreams, thunderstorms...it is all part of parenting! :)