My last two are 14 months apart. I found that having alot of toys kept him busy and I still held him alot when the baby was sleeping. Also, Dad and grandma would love on him lots and so he never lost that special feeling. It's easier the younger they are in my opinion. my older ones take longer to adjust than my toddlers have.
It's not hard at all to have a newborn and a toddler at the same time, in my experience. My daughter was 21 months old when my son was born, and she was a TOTALLY love-spoiled child...total center of my world. I was terrified, thinking she would be jealous or feel replaced. Nope!
She wanted to be involved and help me with the baby...and honestly, bringing him home from the hospital was SO much easier than bringing her home, because I knew what to expect!
Now..having two toddlers at the same time, lol, that's a whole different story - but totally rewarding. My kids (my daughter just turned 3 and my son just turned 1 and I'm due again in April) are super close emotionally and close enough in age that they play with a lot of the same toys and have some of the same interests...so it's really cool to see them play together.
But honestly the newborn stage isn't tough..just make sure you involve your son in caring for the baby "mommy needs your help with little brother/sister...can you hand me that burp cloth? how could I do this without you! what a big helper!" and love on him when the baby's asleep. and if the baby cries you can throw in comments like "wow, that baby sure can cry!" or "yikes, is he hungry AGAIN?" it used to make my daughter laugh and let her realize that it was OK to feel frustrated by the baby, but I showed her through my words and actions how to respond to the frustration so she knew how to react appropriately.
He will feel a little frightened at first..obviously, you're bringing home a whole 'nother attention stealing human being...BUT...like most older siblings, I'm sure he'll be in love in no time! and having your kids close is definitely exhausting as they begin to get more independent but..totally worth it! hence why we're doing it to ourselves for a 3rd time right now, lol.
involve your first in everything to do with your pregnancy, from appointments and hearing bubs heartbeat etc, he's not too young, he may be a little clingy when bub first arrives on the scene but because he will still be young he will accept the new baby, also when he comes to the hospital, let him have a good look and a cuddle and you could also buy him a present from the new baby as well, when you get home he will be interested in the new bub so dont push him away let him be with bub (supervised of course) and the novelty will soon wear off