As my new Mac contains mostly Cloud storage, I stored all pertinent files on an external hard drive, which I checked to ensure could be opened on my new Mac.
The unfortunate thing is that my CS3 version of Photoshop is no longer considered relevant and cannot be loaded on to my new Mac, even though I have the discs, serial numbers, and an external disc drive.
Regardless, I was motivated to accomplish this goal mostly by the possibility of selling my old Mac for casual use or parts. However, the process of guaranteeing security on a computer so old proved to be more difficult than I anticipated.
I learned the following in the wee hours: This computer is too old for an internal factory reset function. I then attempted to manually delete all files before realizing that, even if I were to wipe it clean and do a 35-step secure deleted safe function, the computer would still be inaccessible to a new user without reprogramming. As a result of the aforementioned complication, in order to do this, I would require the original load discs from my 2007 purchase. I spent an hour or two looking for them in any possible location in my place (nevermind that I've moved four times since 2007), but no cigar.
I also learned that, before they were so ancient, Apple used to mail you replacement discs. No longer. I also couldn't find any for this version on eBay.
I stored the computer away in a box for now, incase I should happen to find such a disc in the future. For now, the goal as listed has been accomplished.
Original goal list posted here
