Of course manual gearboxes have park. It's known as 1 or R depending on which way you're facing... ;)

It depends on the car, really. My 2000 Saab required you to shift to reverse in order to remove the key, regardless of the incline.

Not something I was taught to do for my UK license in ‘09, IIRC.

It's one of those things I picked up from when older people taught me how to drive. Presumably from when hand brakes were more likely to fail than on modern cars. Maybe if someone crashes into the car while it's parked.

Either way I still do it. And turn my wheels towards/away from the kerb on a hill as appropriate. Probably useless but if you have a fail-safe, may as well apply it.

Forgetting the handbrake is a common cause of minor accidents. Half the automotive 'fail' videos on the internet are people forgetting the handbrake. The habit of never leaving the engine on neutral greatly reduces the probability of this kind of an accident.

And sometimes even non-minor. Wasn't Anton Yelchin (the Star Trek actor) killed when he got out of his car to open his security gate and was crushed?

For sure, can't risk handbrake failure.

It is not wise to rely on handbrakes. Firstly handbrakes aren't designed to hold any significant load. Just search for an image of a handbrake cable. It is good enough most of the time, but it will bite you once you have a fully loaded car at a steep slope. Secondly it is a good habit to never leave the car on neutral unless you have a good reason because this habit will save you in the event of forgetting to pull the handbrake.

It’s fine if they haven’t driven one, but at least read a little.