There are a number of different hardware options. Both motherboard and chassis.
2*70 mm fanFrom picco.nl Or mini-pc.se.
Initially I planned to make a NAS which was possible to keep in my living room. After moving this was no longer a requirement which made the decition much easier.
I finally chose the following hardware. Very basic setup indeed.
Different software links I reviewed before choosing standard OpenBSD server below.
First I tried to setup NFS. See more information on NFSSetup. But NFS turned out not to be compatible with Apple Time Machine. Therefore I tried an AFS setup instead,AFSSetup, which is working great.