What is the minimal system that would be suitable for this task? What kind of system and OS would you recommend for this?
Requirements for a Full Node
I have found macOS to be the easiest to get up and running in the smallest number of steps. Your mileage may vary though.
Linux/macOS/Windows and anything else that can execute the iri jar.
At least 2 or more cores with 64-bit architecture
At least 4 GB or more
At least 50 GB of free space
2 Mbps or better should suffice
24/7 (or close to it)
Static IP Address
Required, visit here to setup
Setup a GUI Full Node
Visit IOTA GUI Full Node guide
Setup a Headless Full Node
These requirements will change as more and more people adopt IOTA.
If you've ever configured a Bittorrent tracker it has similar system requirements to one of those.
What about Raspberry PI? The best model available right now would likely under perform. The CPU and RAM is a little too weak for the java implementation. There are other implementations in work requiring less ressources, through
My personal recommendation:
Operation System: Linux (generally better for server)
RAM: At least 4GB. Better 8GB.
CPU: Quad-Core x86, ARM is not supported at the moment (I hope it will be in the future)
HDD: 150GB - 200GB, not necessary (just to have big buffer for the transaction database)
Internet Connection: 100Mbit/s or more
Why all these recommendations? If you want to have a secure full-node, you need some more neighbors. These neighbors put pressure on your node. If you want to share your full-node with friends, family, you get also more traffic/pressure because of the light-nodes. But: Just try it with the minimal settings and find your perfect setup :)
So the topic with your Raspberry:
There is a list of supported ARM devices.
Some Raspberry boards are supported. I haven't tested them yet. I have other ARM-boards and I cannot compile IRI on them. Probably the list is outdated (2016). The issue is the RocksDB database not IRI itself.
At the moment 28.12.2017: A node should have at least 8 GB RAM. It's better to have more, because the machine, operating system and other services need some memory for themselves. The Java Memory settings should therefore be set one or two GB below the RAM-Size for 8GB e.g. to -Xmx7G
The node shoud have 4 cores.
The node should have a SSD with around 40GB space. The mainnet DB has around 9GB today, but is growing.