I'm going to be replacing one of my fans, and I figure I may as well replace my HDD while I'm at it. Any guidelines I need to follow aside from 2.5''? Should I stay away from 7200RPM for heat reasons?
Modern 7200rpm drives do not make more heat, cause more vibrations, or use more power than 5400rpm drives. You can use basically any 2.5" wide 9.5mm tall drive.