When to Put New Baby into Big Sisters Room?

I didn't worry about that... I think my second/third/fourth babies slept in a bassinet in my room for a few months for convenience, but were moved into the sibling room shortly after that. (We just had 2 rooms for the kids.... at one point, the oldest got her own room, so for a while, we had 2 girls age 5 and 7, and the infant all in the same room. It was a pretty big room, though.)

The older kids learn to sleep through the noise of baby waking......

Depends on how sibling is handling the new baby. If you see there is no static between the 2, introduce the new living arragement and instill the new behavior. Child #1 will get used to the idea and sounds of child #2. You are the one that knows and sees and knows best.

if the older child sleeps well.. put them together.. but if the baby will wake up the older child keep them separate till baby doesnt need a bottle in the middle of the night.

Try it now. I was pleasantly surprised that my older son miraculously slept through middle of the night wake ups. He also put himself to sleep quietly. So we would do story in my room, and then he would tip toe into bed (baby already sleeping). Once they went to bed at the same time it got much easier, but it worked that way too.

It is recommended to keep you baby in your room for the first year as a preventative for SIDS.

If I had the luxury of waiting, I'd wait until about age 2 when they can enjoy a similar bed time routine and bed time. If I didn't have the luxury of waiting, I'd transition when baby was sleeping pretty well through the night and hope for the best.

We always waited until age 2. But mine don't sleep through until then. Baby #5 will currently have no place to be (alone) so we'll be in the same situation.

If you can wait, I'd wait. We do have two boys sharing and they talk and don't sleep as well (at least it takes longer for them to fall asleep). The girl with her own room? Sleeps like a log the minute her head hits the pillow. No distractions!!