Hi JT!
I hear you about feeling bad to use a piece of history, but your machine was definitely well-loved and used, probably to make lots of clothes for a family, or several families! I think of objects like this as meant to be used, even if gently, like the vintage fountain pens I also collect.
1882 seems the right date; you always go with the higher of the two numbers on the stitch length plate. Patent dates stamped in things like this machine and fountain pens are often older than the things they're stamped on...
Here's how I learned to thread the shuttle on mine:
https://www.youtube.com/watch?v=Ppgunmtq9aU
There are replacement needles that can be found on ebay and etsy and some other sources; original Singer needles for the 12 will be hard to find.
Manuals can often be found online or bought in physical or PDF form from sellers -- here's a PDF of the British version of the manual for your machine:
http://ismacs.net/singer_sewing_mach...12k-manual.pdf
Also, here's an awesome video where a guy discusses your style of cabinet...
https://www.youtube.com/watch?v=eKXDfAX_-FQ
Parts like the treadle belt and even special pliers to trim and fasten it are relatively easy to come by. I've been a little obsessed with my hand-crank 12 on and off for a while. Learning how to bring one of these back into service and then making something with it can be such a joy!
Cheers!
Matt