08 giant trace x2 upgrades

Hello, I'm looking to upgrade my 08 giant trance x2. Brakes, Shock and Fork. I'm leaning on the avid elixir cr brakes can I run there 180mm rotor in the front? The shock i'm thinking of a fox rp23 rear but I don't know what "size" shock i should be ordering, and for a fork I would like to stick with a fox brand air. Can some one chime in and help me with my choices. I am keeping an open mind.