any of your choices will work fine. i suggest the cheaper of the two 6450s. a bit better than the 5450s. you won't need the 2Gbs the 1Gb is fine.
now any other those PSUs will be fine. a seasonic 400 is a good choice. but i would suggest the 430 because it has the power connections if you are able to get a better card like the 7770 later.
you will be able to use that later also but you will still need to upgrade to another low power system (cpu and motherboard) much like with a 400 watt PSU.