An $800 budget works scrape you by, it is about $800 with these parts and a motherboard. 8GB RAM minimum with lots of mods, but for 8GB to be worthwhile, you will need Linux because only Linux has 64-bit KSP. A 4460k i5 is more than enough for 60FPS at most times and 2GB of vRAM is good as well. Active Texture Management reduces RAM usage and OpenGL/DirectX 11 help even more with using less RAM. Anyways, welcome to the forums! With practice, your Kerbals will not die. Much.