I suggest getting a power line ethernet adapter to boost the WiFi signal on the 2nd floor , then a good tiny USB adapter to connect to WiFi. I don't know how it affects ping and so on , but i would read more about this if your wifi signal does not reach you or if it is low.
About your build :
1) Get a 7200rpm HDD preferably black caviar series.
2) The PSU you selected is tier 2 quality PSU , i suggest getting corsair HX750
or another 750w Tier one PSU from this list