My first two children are 16 months apart. I was still nursing when I got pregnant with my second child. As soon as I said, "Okay, let's have another," it felt like I got pregnant! No problems there! I kept nursing baby #1 but with one of my pregnancy symptoms of tender nipples, it felt like I had just started nursing all over again and was too painful for me so I quit, when my first was 9 months old. He didn't have any problem quitting either. I've heard that the milk taste changes a little when you get pregnant so I don't know if that had an effect on why he had no problem switching to formula when he had never had it before. I do know of other's that had no problem nursing until the next baby was born so it is possible.
As for sleep...ha ha! It felt like I didn't sleep through the night for over 2 years! That's why I told my husband, "I want to sleep through the night at least once before we have another baby." Baby #3 came 26 months after baby #2. But you survive! Mommies have amazing strength and endurance!
Tips, make the children take a nap at the same time and you nap too! Stick to routines the best you can. Let baby #1 hold, touch, and love baby #2 (under supervision of course) so that there is no jealousy and they are friends. Get help from others to take baby #1 out to play especially when baby #2 is so little. Let baby #1 "help" as much as possible (go get a diaper...) I've got lots of advice! :)
The best part is that my first two a buddies. I love to see them play and love each other. So much so when one is using the potty the other is there keeping him company. ;) It DOES get easier!