Hey there, nice job on your first build, and I have a few recommendations.
1). First off, I do not recommend getting a 400w PSU if your requirement is 311w, and here's why:
Power supply units do not always run at optimal efficiency, and in fact, normally don't. A normal PSU runs at around ~ 80% efficiency, so (400x0.8) = 320watts of power, which is cutting super close to your cutoff and leaves you no room for an additional hard drive or overclocking.
I recommend getting a 600w power supply, since they will only cost 20$ more or so. Furthermore, please make sure it's atleast BRONZE rating (has to do with its efficiency) or higher (silver/gold/platinum). After my 3rd computer build, I've realized that my overclocks and performance suffered by buying sub-par power supplies. Plus, a more expensive PSU like the EVGA 650w comes with nice black braided cables instead of the ketchup and mustard that come on cheaper units.
On another note, I recommend replacing a HDD with an SSD or getting a cheap one used on ebay. SSD's make a huge difference in what humans perceive as "fast computing". It won't affect your fps in games, but will cut down load times and boot times by an insane amount. Will save time on projects and homework, especially with 11:59 deadlines being tough and all.
2). Not sure if you use wifi, but if you don't have a physical ethernet connection you need to get a wifi card (about 20$ or cheaper) or even a usb wifi chip (aesthetically debatable).
3). Oh and you need a case?
Good luck man, and don't forget an 4). optical/cd drive if you're installing your operating system that way. If not, usb installation is pretty good too.