a rasp pi may work depends on the coin.
if the blockchain is big and you run a master node
you want a very fast drive.
you want to be able to clone the drive for a back up.
you want a windows or a linux not apple
I got fucked by PPC I had an apple they wanted to force a upgrade to the nodes and did not provide an upgrade for an apple only windows
I have 2000 usd worth of PPC which was stake long enough to reach a 99% probability to earn interest so to speak of around 40 dollars.
But I had to upgrade on the node could go dead losing my coins and I could not upgrade since apple upgrade was not give to me .
So I sold off the 2000 in coins for 1960 never got the interest and never did a POS coin again.
So my take is don't do a POS coin
but if you do do it with windows 10 which means
something like this
http://www3.lenovo.com/us/en/outletus/commercial-desktop/thinkcentre/thinkcentre-m-tiny-series/ThinkCentre-M900-Tiny/p/10FMX007USadd more ram and an ssd