How to consolidate the number of computers that run older OS X systems?

How to consolidate the number of computers that run older OS X systems?

Welcome the New Year and it’s a time to clean house … of computers. The straw that broke the camel’s back is High Sierra with it’s new file system APFS that replaced HFS+.

I’ve got too many old computers that are set up to run vintage OS X applications such as 10.4.11 on an iBook, 10.6.8 Snow Leopard, 10.11.6 El Capitan, 10.12.6 Sierra, and now, of course, Catalina. These changes have had an impact on a number of files that I would prefer to keep intact as updating often results in unintended consequences. The other impacts are with older equipment (f.e., scanner, printer) that will not run on a newer operating system because the drivers have reached “end of life” since the manufacturer won’t support their equipment any more. All these older files require backups so additional drives add to the plethora of computer stuff to store and maintain.

So, the hope is to find a way to retain the ability to manage older files with fewer pieces of computer equipment.

The options that I have explored include: #1 having the operating systems on separate desktop drives with the associated files; #2 partitioning a drive on the computer for the various operating systems, and #3 the time-honored  “do nothing” option of maintaining the status quo. The plan is to use Catalina for the boot drive. It was suggested that I use VMware Fusion but after viewing its web page I haven’t seen how that would work but obviously it can. 

As an aside, at the same time I also need to be very careful with moving iMovie and FCPX files (starting with the earliest versions) to other drives so they don’t become corrupted. Currently running MacBook Pro 2012 (mid) with Catalina and Mac Pro 2012 (mid) with Sierra (but with a metal capable graphics card and is Catalina ready). Can’t afford iCloud. RAID, maybe later and not unless it is low cost and not difficult to maintain. Time Capsule or Time Machine? Have a couple old ones but haven’t explored how to incorporate them and the Time Capsule seems to have a problem. The current plan, unless a better alternative pops up, is to proceed with the migration in small steps to a couple (existing) large desktop drives (one as mirrored or backup) that are partitioned for the older and different OS systems then boot via the computer running Catalina; won't need to do this very often. Cheap and easy is to err on the side of the Angels!

QUESTION: How to consolidate the number of computers that run older OS X systems? Suggestions?