It's a great place to start if you are new, although for your prototype it could be considered a little big. If you're going to use it again for other prototypes get the uno or MEGA. If not then shop for something smaller.
Proto-pic is a good UK site, I don't know where you live though.
One issue with this for me.. It will have to be turned on all the time which will use a lot of battery power. Do you know how you are planning on powering it?