For a simple file sharing role, it looks like these settings should be set:

server role = standalone

; don't do anything about names and domains
wins support = no
domain master = no
domain logons = no
local master = no
preferred master = no

; copied from
load printers = no
printing = bsd
printcap name = /dev/null
disable spoolss = yes

; can use direct ip address instead of netbios
; don't forget to disable nmbd (in FreeBSD: rc.conf nmbd_enable=no)
disable netbios = yes