Or do I need to buy (and do some special setup on) a "NAT Router"?
b) If I need to buy a "NAT Router", do they only come as set-top boxes that need their own power supply and service 4-5 client computers? i.e., I'll never have more than one computer, and I'd prefer a form factor that looked more like a USB flash drive, but with Ethernet ports at both ends & power supplied by the PC. i.e., I only need the "NAT" part, not the "Router" part.
c) Many years ago, my company implemented DCHP (Dynamic Host Configuration Protocol) that I gathered somehow re-configures the virtual (though obviously not physical) IP address of my work computer, presumably to improve security, anti-phishing, cyber-attacks, etc., Is it something technical or merely economics that keeps my cable company from implementing DCHP, too?
The address you saw was probably his WAN IP if he's not using a proxy. WAN IPs are issued by the ISP and you have no "say" over what it will be (unless you pay for a static IP from your ISP). Your router is assigned a WAN address once it connects to internet, only one WAN address. The NAT on your router "shares" that one address with all pcs connected to your network when they access the internet. The DHCP on your router simply assigns any pc/device a local (to your network) IP address. You router does use DHCP and so does your ISP.
Both NAT and DHCP are network terms and not Security terms.
You could possibly find a smaller router on the market, but it will probably do the same as your Motorola.
For someone to find you from your WAN IP they would have to find the ISP which issued the address, then request the information from them. That kind of info is privileged, and can't be accessed by anyone. Someone could find the general area you are in (country) but getting any further would not as be easy.
So basically he sent some code in his e-mail that show you YOUR IP, it does not show HIM your IP. To prove it go to the local library they have free internet, pull up the email and watch it show you a different IP.
that said the only secure computer is one that does not work.