Check out the FAQ, there should be a thread for what you need to install a double DIN stereo. Check out the ICE section to find many stereo installs. There's even a multiple threads for sound deadening your ENTIRE car.
Search is your friend.
And what car did you get? What year, what engine, what trim? I assume 2.5S so you can slow down, and since you need an upgrade for stereo, it's not Bose and you have cloth interior.
As for the center console, I think you are the first person to ask that over the past 4.5 years of being on here with this current generation Altima, so I have no insight on that one. I'd say just avoid putting stuff down there and keep it clean.