Indeed it did help, so thank you.
After some 12 hours of reading, writing, choosing, trying, booting, loosing (do I use MAC address in preference to Hostname? What if MAC address is different for wired and wireless connection, do I use IP or TCP or UDP ... and so on) I am now quietly confident of having no idea whether or not my security is compromised.
And to think this could be done in 3 to 5 interactions, in about 15 seconds, with Windows (non)-Firewall.
And the best joke? It made not one jot of difference; I still cannot do file or printer sharing.
But let's close this post as solved, here.