Mine is 55" on desktop, mouse and keyboard on desktop, I bought a 12 dollar adjustable plastic computer stand from walmart, that holds the joystick, and I have a cherry humidor on the side that holds throttles. I use twist for the r udders, but I use pedals for driving sims, and they fit into the mix just fine.
If your going multi monitor, then your going to have to probably need more then one desk to make everything fit right.
It all depends on how deep you want to get into it, ya know ;p