I finally retired a couple older Macs, although I'm still using the 17" Powerbook to access servers and stuff.
I bought a Mac mini (actually two of them) and am almost finished transferring data, user account information, etc. I still have to move a few OSX mail mailboxes but that shouldn't be an issue. I have the .mbox files, so it's just a matter of doing the imports and organizing.
The only surprise is that Interarchy V10 doesn't work on Mojave. Version 11 Beta is supposed to work on Mojave, but it doesn't. The beta expired so it doesn't launch. I think the developer has checked out because his notes are few years old. Too bad. I was using Anarchy/Interarchy for a long time. So, I'm currently without a FTP program for the mini. It still works on the 17" so that be what I use for a bit.
While doing the transfer(s), I moved WeatherCat from the old iMac and I ran it on my 17" MacBook Pro for a short period. I had the same instability issues with WeatherCat when the FTP upload was turned on. The new Mac mini has been stable. So, there must be an incompatibility with 9+ year old hardware. Problem solved.
BTW, the screen sharing on Mojave and High Sierra works well. I didn't need to be anywhere near the Mac minis to do any of data transfers. Now that I'm practically done, I'll order and setup the Mac mini monitors.