Used from a junkyard? They may have a warranty, dont buy used from an individual

How much money difference are we talking about? It takes 5 quarts right? The tech was doing you a favor trying to get more life out of your POS…its a habit that they put in a better oil, tell him your sorry, and that you just got fired from work for always being late. Next time you should specify when you have oil service for them to put in the crappiest oil they carry. And yes remember what Obama was doing to thousand of cars, killing the engines in exchange for some crappy cash for Clunkers program. Just use less of that engine poison.

Yes a pad set, inner and outer pad for one caliper, one side of the vehicle. And when you do both sides put on ceramic pads

It would bug me if I left it like this, the problem was, I bet, that you did not use a short extension on the socket, its very difficult to hit a socket squarely if you don’t use an extension.

I would get it out, if it makes it way to the drain hole your door could fill up with water.

What manufacture warranty do you have if its only 50,000, you might still be in warranty, its from the date of purchase.

Autozone will let you borrow their tools to get the job done, unless you have a 1/2” breaker bar, it will be difficult to get the caliper frame off, meaning you can’t replace the rotor, I would just but some caliper grease and pads and brake clean, see if you pins are stuck in the caliper, lube them. Then replace the rotor at home.