Best I can do for ~$400?

I'm building a PC just for gaming/normal use. I'm going to be ordering the parts in the next few weeks and just want your guys' imput. My friend is giving me a dirt cheap case for free as well as a copy of Windows 7, and I have an 80GB HDD I will upgrade when I get the money. I prefer not to go over the $380 (I need a new hard drive and monitor[I'm using my tv for now]). Parts:

GPU: Sapphire 7850 - $145 (Newegg)

CPU:AMD Athlon X4 750K Trinity 3.4GHz Socket FM2 100W Quad-Core Desktop Processor - Black Edition AD750KWOHJBOX - $80 (Amazon)

Motherboard: MSI FM2-A75MA-E35 FM2 AMD A75 (Hudson D3) HDMI SATA 6Gb/s USB 3.0 Micro ATX AMD Motherboard - $56 (Amazon)

Ram: CORSAIR Vengeance 4GB 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model CMZ4GX3M1A1600C9B - $38 (Newegg)

PSU: Corsair Builder Series CX 600 Watt ATX/EPS  80 PLUS -$58 (Amazon)

Total: $377

I was hoping the power supply will last me 7+ years because I don't plan on using more than 1 GPU for a long time, so is this corsair the best PSU for that plan?

Is the FM2 socket somewhat future proof? Or should I try to switch to AM3?

 

somewhat future proof, with things like the entirely new line of apu's coming out, which i believe are up to 8 cores with integrated graphics, and i also believe that they are on fm2, although i'm not sure about either of those things.

 

If I remember correctly, Corsair has a 7 year warranty, so you should be good there. Not to mention that they use Seasonic power supplies which are top notch.

The FM2 socket should be fairly future proof. AMD's not going to be getting rid of their APU's anytime soon, but it's not like they're performance parts either.

I'm assuming that CPU comes with its own heatsink?

Yeah it comes with a stock hintsink. I don't care about performance parts; I just want to play modern games at 1080p (1440p in a few years).

You forgot the case

From what I've seen, FM2 and AM3+ are not getting anymore CPUs/APUs. It looks like all Steamroller CPUs are going to be on FM2+, sadly FM2+ CPUs will not be backwards compatible with FM2.

tl;dr: Don't worry about getting a future proof motherboard because it won't be compatible with any of the new CPUs.