Welcome to TN.
Check to see if your car has the prewired amplifier bypass harness. You'll have to pull out the CD player to check.
http://www.toyotanation.com/forum/t70082.html
The harness to buy that plugs into the prewired bypass harness is linked in that thread.
The front doors have a 6x9" mid in the door. I believe the dash speakers are 3.5" I could be wrong though, it could be smaller.
There are several different steering wheel controls adapters available from PAC
The PAC SWI-X is a univeral one that should work well for your headunit.
This adapter works for your year(Gen5.5) camry
http://www.cardomain.com/item/SCOTA1468B