My toddler was almost 18 months when my 2nd baby was born, some advice i could give is don't expect too much! Don't expect everything is going to be the same as with your first baby... every baby is so different. Don't expect your toddler's is going to stay the same, his sleeping patterns and behavior is going to change. He will most like cry for your attention when you are busy with baby. It is going to take some time adjusting for them too having a little brother or sister.
I found with my girl that she was so inlove with her little sister but obviously she didn't understand that she can hurt her if she touch too hard or poke her eye, but keeping her away was impossible so if I allowed her to touch and interact with her sister she was happy but I had too keep showing her how to be gently. Also involving her with everything like nappy changes, she was able to get a nappy and even undo baby's clothes so she felt very important helping me. And also alot of one on one playing with my toddler was very important when baby was asleep so that she didn't feel left out. After the novelty of having a new baby sister wore off a bit she was happily playing on her own again but still wanted to be picked up or cried for attention espesially when I had the baby in my arms.
And to be honest don't expect much sleep for the first few weeks, it will getter once you have some sort of routine going. My toddler now goes to preschool for 3 hours 2 days a week and i love just having that few hours to do something or just to have a cuddle on the bed with my little one, which is something you might not get to do often with a toddler.
And most important don't ever leave your baby unattended with your toddler, even for a moment. If you have to go to the loo, put baby in bassinet or cot safe away from toddler, mine has tried several times to put various things in baby's mouth.