There are many schools of thought on what you are asking. Here is the best I can offer hope it helps.
Do not give your 2 year olds room to the new baby. By doing this it can cause some psychological problems for your older one feeling like he has to "move over" because of his new sibling. He is already going to feel this way in a sense because of the time you will need to nurture the new baby. It is best to try to engage your first born by asking for assistance with the new born - not give his personal space away. (especially moving him all the way downstairs)
Most likely you are going to want to have the baby sleep in your room for the first few months anyway so I would wait to see how things unfold. You cannot plan everything too soon.
As far as a theme go with Animals and bold colors all kids like animals. I did not want to find out the sex of my child and that worked for me. Babies R us is a great source.
Toddlers are just getting out into the world. They are really dependent on their parents and you may find that he will end up in your bed a lot. How you handle it is up to you.
I have a 7 year old (only child) he sleeps with us almost every night since he has been born. He feels secure this way. In my personal opinion I feel it makes him very secure. Comparing him to his friends he has a lot of confidence and is not afraid of trying new things. If he had a bad dream I usually don't find out till the next morning because when and if it happens he wakes up and finds me or his father and snuggles up. No tears in the middle of the night. (we get good sleep too)
I usually ask parents what animal in the world DOES NOT sleep with their young? - Only one, Humans.....I wonder how natural that really is for us to be in a room by ourselves with our parents so far. As far as the intimacy goes believe me there are other places to "do it".
Make all the noise you want we sure do! I swear my child can sleep through an earth quake and he is used to it. Hope this helps.