Just getting into this stuff and I have a question about the relay shield. I want to do more than just control some relays; specifically, control a motor. I’m getting the impression that I’d want to use a separate relay instead of a relay shield.
Can the spark core use both the relay shield and do other I/O as well?
Yes sure it can 
On the relay shield, there are pads for you to easily access the other pins not used for switching the relays.
If you are using your own relay, you can use the pins on top of those for the relay
If you have an unused relay on the sheild, you should be able to use it to control a motor.
If you want speed control, then you’d need to use an output from one of the other Spark Core pins.
Not 100% sure about this, but if you have 2 additional relays free, you could even use them like an H-bridge to reverse the direction the motor spins it. (Please double check this, as maybe this could result in shorting out the power supply? Not sure.)
cya
R
Note: If you plan on using I2C you’ll be better off with a separate relay board, unless you cut the traces to D0+D1 and jump them to a separate set of pins