Thanks everyone for the valuable info.
As Artie505 correctly surmised, I hadn't been using Time Machine. I was just doing manual backups of important files to an external HD. However, as of today, I fired up Time Machine, and will be using it henceforth. So, I'll have a good backup in case things go awry.
Checking over what I have for applications that haven't been updated for a while, I see that I only have:
Filemaker Pro Advanced 9
Vectorworks 2009
RealBasic Pro 2009
Everything else is either shareware or is up to date and should work with Yosemite. Checking the hardware requirements, I see that I need a minimum of 2GB of RAM, which is exactly what I have. Is this running things a bit tight, or should I be looking at adding more RAM? RAM appears to be fairly cheap these days anyway.
