I finally got everything up and running as I'd planned - well, almost.
1. I have the dual 500 MHz "Mystic" Power Mac G4 running as a Web server using MAMP. It took a little digging to figure out how to enable Server Side Includes (SSI), but I did it. I'm using ZoneEdit.com for dynamic DNS, and eventually reformed.net (a personal research site) will be served by this old Mac. Until then, it's available at reformednet.gotdns.com courtesy of DynDNS.org. I'm using DNSUpdate to keep ZoneEdit and DynDNS connected to the server. All of these apps and services are free.
I decided some time ago to move reformed.net from AIT Domains, where it has been hosted for several years. Their servers have been compromised, the website has been infected with "badware" links, and all sorts of services (including Google search) now flag it as a "reported malware site". My solution: Run my own secure server.
2. I swapped the external FireWire drives between the dual 1 GHz "Mirror Drive Door" Power Mac G4 and the dual 1.6 GHz upgraded "Digital Audio" Power Mac G4. The upgraded DA has been my primary machine, but with the CPU upgrade it doesn't want to boot Mac OS 9. The MDD is a bit slower but will boot OS 9 when I need to. I did swap video cards, so the better card from the MDD is now in the DA.
I now have two monitors side-by-side, each connected to a different Mac (one running Mac OS X 10.4 "Tiger" for Classic Mode, the other running Mac OS X 10.5 "Leopard" so I can get used to it and use some newer apps that are not compatible with Tiger), and I can more the mouse and keyboard from one display to the other thanks to Teleport, a great little Mac-only freeware app. With Teleport, you can move clipboard contents between machines and drag files from one to the other. After quite a bit of trial and error, I finally figured out that it only works in both directions when Leopard is the master/host and Tiger is the slave/remote.
3. Everything almost went smoothly. The MDD chose this as the day its FireWire port would fail, so I had to dismantle the NewerTech miniStack and transplant the 400 GB hard drive in the Power Mac. I prefer to work from external drives just because it's easier to move to another Mac if a computer fails, but the dead FireWire ports killed that. (My backup computer is a 1.25 GHz eMac, a nice enough machine, but with only a single CPU, it doesn't run nearly as smoothly as a dual processor Power Mac G4.)