I have a nano size wifi adapter and an el cheapo wireless keyboard/mouse combo, they are useable together, but I would not recommend it. The keyboard often repeats, which I believe is related to the "underpowered" issue.
However, you mention a hard drive. The pi only has two USB ports, so it's physically impossible to plug in a drive, a keyboard, and a wifi dongle. If you are considering an adapter/unpowered hub to increase the number of ports: don't bother. As is, the pi does not come close to meeting the USB 2.0 power standard (500 mA per port); I don't see anyone claiming you can expect more than 150 mA TOTAL. If you have a good reason to believe you can plug in a drive and have 200 mA left over, please share it.
Otherwise, if you want to do this you will need to use a powered hub. If you are intending to use this rig as part of your education campaign, I recommend against the pi. While it was designed for educational purposes, the educational purposes it was designed for involve educating people about computers and electronics, and not serving as a general purpose computer. By the time you include a display, SD card, keyboard, wifi, a drive, and the powered hub (and/or power supply), you are up into three figures -- for that money you would be better served with a cheap Android tablet or netbook, which are intended for general purpose use.