As Bert mentioned, I would not make diffusion in your control room a priority. If budget is a concern you can create an accurate monitoring environment without using diffusers, and instead pour your room treatment budget into legendary bass trapping.
Instead of rugs on the floor, absorption on the ceiling is a better approach to kill flutter echo. Carpets suck high energy out of your room, but leaves energy in the mids. If you're building a neutral room, for any absorption of high frequency energy you want equal absorption of mids (and of course in a small room like this, you want insane bass absorption).
Scott's suggestions look good. You definitely want absorbers on the back wall since your room is too small to properly exploit the initial time delay gap. I would also consider soffit-mounted bass traps as a space efficient way to add extra low frequency absorption. If you're lowering the decay time in the high frequencies you need seriously bass trapping to complement it. Otherwise your room will be effectively dead for only mid and high frequencies, making low frequency modal ringing problems even more noticeable.
For your live room I think diffusers would be worthwhile (after you've applied other acoustic treatments). If you want some cheap, easy to build DIY designs, check out my site for these free sound diffuser plans: http://arqen.com/sound-diffusers/
. These are modular, optimized stepped diffusers that I've designed specifically for DIY construction.
Hope this helps!