Go nuts.

Yes why not. I’ve used paperclips and even solid core network cable strand before as well.

If it fits it sits.

Seems fine in a pinch. Everything is so low (voltage and current both) that I don’t think it matters too much. Plus breadboards imply temporary tests. If you’re doing something more permanent like a breadboard CPU like Ben Eater then probably not.

Can you? Yes

Should you? Probably not. High resistance and bad contact

I don’t know, can you?

You know the wire-reinforced plastic strips used to secure plastic bags with twisted ends like the ones sliced bread is sold in? Just used four of these in a project.

Yeah, that ought to be fine. Breadboards aren’t rated for fast signals or large currents. So not really a concern.

Network cable is a good cheap source of jumper wires. You can also save the bits of tin that you clip off various components – over time you’ll end up with way more than you need. These are easier to bend into shape.