The 350watt should be able to carry your system ok, 520 would pretty well be over kill for the system. Perhaps you could upgrade the Psu later on id reccomend an Antec true-power 420 i think they call them, its a great Psu. As for Desk , Do you mean a computer desk if so i wouldnt buy one on-line i doubt the saving would be worth the freight component
LJ