Concerned he'll feel replaced. :(

Sharae
My husband and I will be having our second child in January. Our son is 4 years old and so excited to be a big brother. We know this is going to be a big adjustment for all of us, so we've been involving him every step along the way. Including making room for baby. Our house has two bedrooms upstairs and two downstairs. Our master is upstairs along with our sons current bedroom. My husband and I want to paint, add new flooring, and let our son help decorate one of the downstairs bedrooms so that we can have the babies nursery right across the hall. When we talk to him about it he seems excited to help us paint, get a new bunk bed, and help decorate his "big boy" bedroom. But then he says "But I don't want to sleep down there cause it's scary." Im pretty sure once it's all said and done he will love his new room, and he won't think it's scary anymore, but what if I'm wrong? What if he feels like we kicked him out of his "safe place" so the baby could be there. I'm just worried he will be sad or upset and resent us or baby. Am I over thinking this?? My husband says he'll adjust, and love his new room. I just don't want my boy to feel like he's being replaced or forgotten. Has anyone dealt with a similar situation? Thank you in advance for your suggestions and/or opinions.