You can add a hard drive cooler if you wish. All your temp seem to be fine. I would try to bring the CPU temp down if possible. Perhaps a better aftermarket heatsink/fan combo. There's no room in the back to add another exhaust fan?
When running exhaust and intake, it's better to have an even amount of each. I have two intake from front, one side fan as an intake too, two rear case exhaust, and a system blower in the middle (PCI slot). My CPU's at 30 degrees Celsius as of this moment.