GPIO and relay quesiton
That might work, but I wouldn't recommend it. You activate the relay by making the input on the module low, but I don't know if the RPi can sink the required 15~20 mA(*). But the problem is when the relay is off: the LED should drop the 5 V to an acceptable 3 V level, but since there's no current flowing the I/O pin may see close to the 5 V supply. Which it doesn't like.

I would recommend using an NPN transistor, with a 1 k&Omega; base resistor.



(*) The main reason I'm reluctant towards the RPI is that there doesn't seem to be a real specification, other than the information gathered by third parties on the 'Net. Broadcom also doesn't seem to have a public datasheet of the SoC. I don't buy a product under those conditions.