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.
Maybe Banana Pi is a better bet. It has 1GB RAM.
I very much would like to get some Pi's myself to help support the network. Sadly i don't know the first thing about setting it up - anyone fancy writing a tutorial on the nem forums? Prwetty pwease?