I've finally decided I needed a new system, so ordered a new iMac and a new Time Capsule.
The new Time Capsule has 3 TB backup storage and automatically and periodically backs up everything connected to it. I am in the process now of copying my old backups over from my old (2TB) to the new ... according to the status bar, it should be finished in about 16 hours!
The new computer is supposed to be here by the end of the month. I will set it up in parallel with my current system so I can copy over any necessary documents before wiping the old one to give to my daughter. I have a feeling that's going to take a while as well.
The new iMac:
27" iMac with Retina 5K display
4.0GHz quad-core Intel Core i7 Turbo Boost up to 4.2GHz
32GB 1867MHz DDR3 SDRAM
3TB Fusion Drive (incorporates a 128GB fast flash drive as a buffer.)
AMD Radeon R9 M395X with 4GB video memory (would prefer nVidia but they didn't offer it. )
Apple Keyboard with Numeric Keypad
Logitech G900 Wired/Wireless mouse - sorry, Apple just doesn't have decent mice!
Yes, I think I'll be happy with it for a while. It's bothered me that the Windoze machine I built was faster than my iMac. Hopefully this will even things out again.