I have a similar setup to what you are proposing.. i went from a Mac Mini to a PC... if you do want to do light gaming, avoid the Mac Mini.. i had mini+xbox and consolidated into one PC and couldn't be happier.
I found most of the noise to come from the stock fan, i also have an i5 Haswell and replaced it with this: http://www.quietpc.com/nh-l9i (Noctua Ni-L9i) and then replaced my case fans with 3 of these: http://www.quietpc.com/nf-s12a-pwm (Noctua NF-S12A PWM Ultra Quiet 120mm PWM Cooling Fan)
I think it cost me £90+ for the cooling stuff but now the PC is whisper quiet, i can only hear the flow of air if the room is silent. It keeps the case so cool i barely even hear the GPU fan when gaming. worth every penny and can't recommend Noctua enough, truly a premium product.