The 2500k is great for overclocking and has better integrated graphics but if your not overclocking and don't need integrated graphics, the 2400 should suit you fine. You will be able to overclock it a little bit but no where near what the chip is capable of.
If what you have is within your budget, then I think you will be fine. Though, if you are not overclocking, you won't need the aftermarket cooler. The stock cooler will work fine. I would use the saved money and buy a better graphics card that will help you out with games down the road. At only 1680x1050 though, the 5770 will do fine. for a little more, I would recommend the 6850.
As for the motherboard, personally, I would buy an ATX rather than a micro-ATX because you will have more expansion slots with the option to add in cards down the road. Additionally, the H series includes integrated graphics that you don't really need if you are purchasing a discrete card anyways unless you want it for a backup.