If you want to move him, it will be easier the earlier you do it in terms of him not resenting the bub for taking "his place" in your room. Does that make sense?

Id do a themed room too, with something he lies and make it really special cos he is a big boy and going to be a big brother etc. He needs to feel safe in there.

If you are in a situation where there is more than one bedroom to choose from, letting him choose (assumng he copes OK with choices) between 2 may also help.