You mention limiting the router to allow 3 connections but lack any details beyond "set it".
Seeing as I see it varying from brand to brand I can't give specifics. On my Dlink all you have to do is tell the router to allow IP addresses from whatever to whatever. It automatically uses DHCP for the address range of 100-254. You can change it to use more less or 3, 2,5 or however many you want. Then the rest is obviously on the PC side.
Call it paranoia if you like, really it's the difference between being a good network tech and a mediocre one.
You're entiled to your opinion like everyone else. If you think subnetting for 3 friggin PC's at home makes you a networking guru whatever. I call it overkill to the nth degree and if you really think your homenetwork is inder so much fire/hacking....whatever. Enjoy you cute hat.