First of all, really great project you have here! Thank you for all of your work! And especially, thank you for being civilized and sharing it under a Free Software license!
I read in at least one place that you recommend Arduino Mega with W5100. I may get to that eventually (after adding multiple TX/RX devices) but to start out I just want to do 315/433Mhz TX/RX. Do you think there are enough resources on an Arduino Nano for that (I guess I would use a Nano, at least in testing, as it would be easiest to power for something that will be plugged in all the time)?
I am imagining the IP stack is the limiting factor / biggest bit of code?