I've been going over and over some of these options for a new gaming rig. I'm pretty confident the main concept if ok, but is trying to squeeze in a 64GB SSD for an OS/Main apps drive worth it for perfomance? Taking a gamble going with a refurb HDD but it will be for storage more than direct app access.
The performance increase from the SSD would be noticed only in loading screens and when you boot up your PC/load programs. FPS in games won't be affected.
430W is fine for the i3-2120 and HD 7850, the i3 is 65W and can't be overclocked and the HD 7850 is ~120W. The rest of the PC would bring that up to 250W max. They suggest 500W for the HD 6870 because it consumes around 180W at load and someone might pair it with a 130W CPU or something. In that case, 500W would be wise.
Try putting your build into this if you want further confirmation: