Computer upgrade

Hey guys, I decided recently that I want to upgrade my computer to a level where it’ll last me another couple of years of gaming and the like. Here’s a list of everything I’m getting for it:
Power supply
Hard drive
External hard drive
When I showed this to my friend he recommended I get a new chassis for heat issues. Right now I’m running a 3.8 single core processor, so the 3.2 quad will definitely up the temperature. Do you think it’s necessary to get a case with better air flow? (My case right now has 2 fans, and a spot for a third.) Also, if you notice anything else in the list that you think needs fixing, please let me know!