Aww OP, so delighted for you, congratulations! Even if you've been trying it still comes as an "oh shit" moment when number 2 is on the way - was for me. DS was 2.10 when dd arrived and I was 37.
It's hard work, but for me not even close to as hard as going from 0-1 dc. DD just fits in. And it is just amazingly lovely watching them together. DS adores DD and aside from food sharing (!) it's mutual. DD is 15m but they'll play a bit together and watching them giggle in the back of the car is priceless.
It does change the dynamic, but mostly in a good way.
The first 6m with DS were incredibly difficult. He woke every 45 mins for nearly 5m. Bf well but v v frequently. Probably had reflux. Was a fairly classic high needs baby. DD has been relatively easy, but I've also stopped trying to do it "right", so I coslept til 8m from the start and did a lot of baby wearing.
I have to say the experience of having DD has been quite cathartic in that I knew what I was doing and felt it loads easier to just enjoy it. That green poo, the growth spurts, the crying at 2am, they don't phase you because you've been there and done that.
So, many congratulations again OP. It's a real adventure and privilege to have 2 little ones. It's hard work but it's bloody wonderful.