I run .28's in my pimped-out Broxa. Runs more like ~350 fps with .20's than whatever it is that they say on the website. But FPS is not everything- 350 is fine- just shim the mechbox and change the hopup (and barrel too if you have the $ for it).
Get your BB's from the BBBastard (ASC name "Scarecrow"), or just buy them at the next game you go to- most games have BBBastard reps or other suppliers. Just ask on the game thread before you head out.
Also search around on the forums for other stuff about the Broxa, like this thread:
And the Broxa is 100% TM compatible, if you were wondering.