Tidal disruptions have been, yes. They are also simulated in supercomputers and they were predicted decades before they were observed!

The direct “swallowing” of a star by a billion solar mass black hole has not been observed. One way to think about it is this event would just involve the center of the galaxy decreasing in brightness by 1 star’s worth, whereas a tidal disruption event is like fireworks - a lot of energy gets released and if we happen to have a telescope checking on that galaxy at least every few weeks, we’ll see it.

Yep. The people who run relativistic simulations of black hole mergers check whether there’s any point at all where a bit of information that was once inside one event horizon can escape, and the answer so far has been no. It’s a good question though and we weren’t super sure until we checked.

Exactly right - the more massive the black hole the gentler the tidal forces at the event horizon.

For example, stars can be torn apart by a million solar mass black hole, creating tidal disruption events that have been observed in synoptic surveys. At a billion solar masses though, the black hole swallows stars whole because the tidal forces aren’t strong enough to disrupt the star before it enters the event horizon.