Bro, this is nowhere near 500watts not unless this rig is OC'ed like hell...

my estimate is somewhere near 300 watts and that includes your monitor...
my 3570k (stock) and no video card only hovers around 60 watts and around 120watts at full load. now let's add 100watts for your 7850 and then another 50watts for all others... that is still less than 300watts...
im using Omni digital power reader by the way... for your monitor, estimate nako ana around 20watts... may samsung P2250 is rated 40watts but i lowered down brightness to 30% and it only consumes 20watts... since yours is LED, it should only consume around 20watts as well...
given that, i think you're safe with 600VA or 650VA for a little more allowance...