There is also a stripped down version with 256MB of RAM. http://www.raspi.today/raspberry-pi-model-a-plus-out-now/ The model A+ has only 1 usb port and no ethernet, so it would additionally need a usb hub and a usb Wi-Fi dongle. Does the model A have enough memory to run NEM?
I think 512MB is more suitable. I believe the RAM footprint for NIS is 512MB to run properly. 1GB would be good though but I believe 512MB is the max.