The PSU will get cool air from outside the case but won't help exhaust hot air from the top of the case, however, the 900 has ample exhaust at the top and rear of the case to counteract this.
The PSU being mounted on the bottom may try to eat thick carpets and dust though!
I have three drives mounted in the lower drive bay of my 900. The lower fan sucks air in over the drives and onto the PSU. The PSU fan pretty much has to just take care of itself. The other front fan, the back fan, and the large top fan take care of everything else. I do not have a side fan mounted.
I am running a 650 watt Antec TP3 at around 60% load. PSU exhaust air is less than 2 C. above ambient.
With all the fans set on High, the thing sounds like a freaking vacuum cleaner. Fortunately, at least in my case, higher fan speeds than Low do not improve cooling.
Antec 900 case does not come with a system speaker.
Here's a pretty extreme example - in terms of work - of what can be done with cable management with a 900.:http://www.xtremesystems.org/forums/showthread.php?t=126395