I know you mentioned the different sleep schedules in your posting, but I still wanted to share my experience. My son was 2 when my daughter was born. We also wanted them to share a room while they were little to leave our home office intact. However, they had different plans. Since they were on different sleep schedules neither one of them got enough sleep and would be cranky all day long. My son wouldn't be quiet while while the infant was still napping and the infant didn't sleep all night until she was 10 months old so everytime she woke up crying it woke up my son and then I had both children awake at 3 am. We ended up separating the children because no one was getting any sleep. Two years later, my children are still on different sleep schedules. My son is an earlier riser and goes to bed early where my daughter is a party animal and will sleep in. Their nap schedules are even different. My son naps in the late afternoon and my daughter is down for a nap around 10 am everyday. It is difficult to get anything done because they get up, eat breakfast, daughter takes a nap, eat lunch, son takes a nap, playtime for all, eat dinner and then start getting ready for bed. Our days are very scheduled.
Anyways, good luck with the room sharing. I have heard some wonderful stories about it where the children grow up loving it. In our case it just didn't work. Let me add that neither of my children like to sleep in any other locations except their beds and all doors and curtains must be closed when they go to sleep. They are the silliest kids. It is great that we don't have them wanting to sleep in our bed, but it does have its drawbacks. If one of them pees on their sheets during the night, we have to change the bedding. I have tried to tell my son to just sleep on the coach and we will do it in the morning when everyone is awake, but nope that is not good enough he only wants to sleep in his bed.