Unless you are overclocking, the stock heatsink for your i3-6100 cpu will cool it just fine. Here is a great Linus Tech Tips episode where Luke specifically addressed that for people not overclocking the stock intel cooler works well https://youtu.be/c66inwtS8_E. Aesthetically, stock coolers do not look amazing, but if you do not plan to have a window in your build, that probably does not matter at all. Take a look at this
http://www.tomshardware.com/forum/327420-28-intel-intel heatsink thread that addresses the same question. They come to a similar conclusion.
All the best for your movies/gaming build! Those new i3-6100's are turning out to be great cpus.