Room sharing?

We live in a city townhouse where our guest bedroom is 2 floors is down from where our room is and also from my sons room. For this reason we plan on having baby number two share a room with baby number one. Our son will be 18 months when the new baby is born, we do not know and will not find out the gender until baby is born. I was planning to wait to order a second crib until after the new baby is here because if it's a girl I would like to do a round white iron crib with a canopy that I have always dreamed of. If it's another boy I will probably just get a more simple style crib. Does anyone have any tips or tricks for setting up two separate crib areas in a nursery? Also any other tips for room sharing with two little ones like this?