what will be the memory medium ? I think the best option should be microSDHC slot - microSDHC are cheap, and small. about the external devices, I recommend to use:
2 usb connectors - for digital PC joysticks
1 usb connector - for PC optical mouse
1 usb connector - for PC keyboard
together - 4 usb connectors, but the optimum way should be to use just one connector with external hub, so all devices can be connected to one usb via hub, the data rate of usb 1.1. should be enough to host all 4 devices.