Right Ok thats understandable and I will try to answer those questions the best I can for both ideas.
The thermometer idea will have the Arduinos placed about 5 meters apart and will be traveling through standard house interior walls. I plan to power them via the mains power sockets so that they get all the juice they need. As for reliability and noise I am not sure. The reliability needs to be fairly good but not to a huge degree, and as for noise I guess just standard house stuff, wifi, microwave, phone etc.
Next is the dot counting idea. This time the Arduino's will be placed very close to each other, like a hand or arms length away. Again they will be powered via the mains and the noise will be the usual stuff. However the reliability needs to be greater as the answer must be correct every time.
Thanks or the Module info, I will take a look at them both!