1. Same with the previous reply, I would go with 1600 ram.
2. there would be alot of room for GPU upgrade. If you could shell out some more cash to upgrade that gpu, for me, at least a 7850, then that would be better for a balanced build.
3. I'm not into MSI boards as they are not known in making good boards. I would go with an asus or Asrock board. An asrock h77m will do for your build.
well i went with 1333 because in regular use 16000 is only around 2% better. i heard that 1600 is only useful for OC and since i wont being doing that its fine. but im no expert i saw this on a website