It might help to put this in context:
http://daemonforums.org/showthread.php?t=9807
I only use NFS when on wired Ethernet. Is that, also, what you wish to do? If so, there's nothing special about either the client or server configuration. No 'knobs' twisted.
I happen to use a separate VLAN for NFS traffic, as this makes the traffic easy to secure. If secure data transfer is needed, either IPSec or an isolated LAN/VLAN are the usual choices.
All Unix-like and many other OSes can be NFS file servers, even Windows. One chooses the file server OS based on many factors. You asked about FreeBSD and FreeNAS, which is FreeBSD-based, and some may choose FreeBSD/FreeNAS because of ZFS, which you state you are not currently interested in deploying.
I happen to use OpenBSD for my NFS servers, because those servers provide additional services and OpenBSD is what they run.
If you do elect to serve NFS to OpenBSD clients from non-OpenBSD servers, take note that OpenBSD's kernel client does not support NFSv4.