ako I go for higher PSU kahit na ang need lang ng system ko is mga 500W or so lang, I buy 1000W PSU 80+. ang PSU kasi in the long run, it will of course no longer produce the max capacity and since hindi naman ako lagi nag uupgrade ng todo, I prefer to keep the parts in my PC intact for a longer period. ang problema mo kasi sa PSU hindi mo alam kung tama pa ba ang binibigay na wattage so pag nataon na kulang ang binibigay niya, possibleng masira ang ibang components (i.e. mobo)
sa video card, maybe palitan mo into something higher a bit something around GTX600 series
for the RAM, if you are planning to add more later then ok yung 1x8GB, but if wala na, you should get more out of 2x4GB because of dual channel
palitan mo rin ang mobo, H61 is a bit old. go for the newer H77 or Z77/Z78 series
finally sa monitor, you might want to consider something like 23 inches so you can get 1920x1080 resolution. yung 20 inches I dont think aabot ng 1920x1080 ang resolution