Congratulations OP! I have 2 DD's 16 months apart.
The best advice I could give is to keep your eldest involved with caring for his new baby brother or sister, and praise him as much as possible when he does anything that makes life a bit easier for you.
Spend quality time with DS when baby asleep - even if it is just having a cuddle and reading a book, that way he wont feel left out when you have to deal with baby. I found juggling life with a newborn and toddler much easier as my youngest loved to sleep, so my eldest got lots of attention.
My eldest DD would get her dolly to feed when I was feeding baby (although she copied me and tried to breast feed her dolly, cute and very funny to see!) and would always cuddle up with me to stroke her sisters back to stop her from getting a sore tummy.
As they have grown older the challenges have become more, but not by much. Because the age gap is so close they are into the same things and now aged 3 and 4 are best friends. My eldest tells her little sister that she taught her to talk and use a fork etc, and my youngest is always very pleased about this. They will have a new brother or sister in September and they both fuss over my growing bump and cant wait to look after the new addition and teach him/her all about growing up.
I would suggest getting help with meals (lots of pre-cooked and frozen meals for the very early days) or have some one help out with DS for the first couple of weeks until you find your feet.
You will be fine and amaze yourself on how well you will cope. Very best of luck to you and your growing family xx