sacsr,
"Can I take MacPlus-appropriate software from the internet, burn it on a CD on my Mac Mini, and load it into the Mac Plus?
Yes! : ) That simple. The Plus was the first 'business Mac' and I loved it until I got a dual floppy SE with an external SCSI HD and an excellerator card with a math co-processor. It was a very capable computer. But, as soon as you used a faster Mac, you never went back to the Plus. You could fix lunch while waiting for disk swapping to boot and load MS Word 3.
What we are saying is that the SCSI bus on the Mac Plus has far more options available for someone shopping for resources.
We have over 300 Macs of almost every model. We have been given over 100 floppy drives. We shop at government surplus stores and auctions. In all that stuff, we only have a couple of 800 k drives but hundreds of SCSI devices. They are SO much easier to find and are so much cheaper to buy and customize.
If you can find a Macintosh 800K (M131) floppy drive, great. Then you also have the problem of finding double density floppy disks ( high density disks with tape over the hole are not reliable in the older drives.)
here is a website with the whole list:
http://www.mandrake.demon.co.uk/Apple/drives.html
I remember buying an 800k floppy drive new in 1986 for several hundred Dollars. The external CD-ROM drives sold for $300.
It will probably be much easier to find an Apple 300 or 600i CD-ROM drive that should read CDs burned in your modern Mac. Your original question was about floppies. The real question is "How do I get data from a new computer to an old computer." That question offers more possibilities. I am suggesting a better and cheaper alternative. Having fun with older equipment requires purchasing intermediate equipment.
Jim