Congrats!
We have a 13 month age gap and although it wasn't planned like that, I wouldn't have it any other way, now. I love it.
It was hard to begin with, especially as Chloe hadn't started walking when Ollie was born, so I was having to lug two littlies around. But I made sure I had heaps of support, and DH took several weeks off work to help look after Chloe while I got breastfeeding established.
My advice is to get your older child as involved as you can from the beginning. Chloe just loves coming and giving Ollie a kiss and a pat on the back when he's crying, and she knows that it's her job to help comfort and care for him, as part of this family. It stops her grumping that the attention is on Ollie, because we are involving her and making her an important role as his big sister. She absolutely adores her little brother. She likes giving him cuddles and helping him to have his bottle, finding toys and his dummy for him when he's upset, etc.
One thing that really helped her as she got to about 15 months to 2 years was her own "Baby". She loves copying what I'm doing with Ollie - wrapping it in blankets, rocking it, singing to it, patting it on the back, etc. I used to give her an empty jar and spoon, and set her baby up with a bib next to Ollie while I was feeding him, when he started on solids. She found it so much fun to "feed" her baby when I was feeding Ollie, and it gave her something to do instead of fussing that the attention wasn't on her.
One thing that's important I think is that she has a few special toys of her own, that she doesn't have to share if she doesn't want to... like her glo-bug and her my little ponies. They are her special toys. And Ollie has a couple that Chloe knows are his special toys as well.
Now that Ollie is getting much more interactive, it's getting really fun. Chloe absolutely loves when she can make her adoring little brother laugh and smile, and (most of the time) enjoys sharing things with him. Of course she gets a bit annoyed when he starts playing with something that she is playing with, and now says "no, ollie, no no no... that is CHLOE'S toy", lol.
Overall it was not as hard as I expected it to be, and I absolutely love the age gap and how close Chloe and Ollie are. They love each other's company. It was hard work in the early days, as with any newborn, so make sure you have lots of support for when you are getting breastfeeding established, and so you can try and get some rest (it's hard to rest while baby is sleeping, with another baby to look after)!
All the best, it's an awesome journey and you will love it