It's all going to get crazy when the new baby comes anyway so I'm not sure theres much value in worrying or making a perfect plan ahead of time. Not that I listened to that before DD2 came.
After the new baby, I would nurse the baby while DH got Lydia ready for bed and read to her. Then DH wore the baby in the Ergo while I nursed Lydia to sleep. Then I (rarely) reveled in the fact that no one was nursing or ran to fetch the baby and started nursing some more.
Even if we'd had a better Plan, I'm not sure it would have helPed bc Lydia really struggled for a while, only wanting me, started night waking all over, screaming for hours in the middle of the night. It was just something she had to work through and it wasnt painless for anyone involved.