1. As far as tournament grade lists go, prepare to be dumbfounded. The top marine lists either play like guardsmen hordes or invincible psychic deathstars, and several of the xeno races take multiple copies of amazing monstrous/gargantuan creatures like riptides, flying hive tyrants, wraithknights etc.
Many armies, at least half of them, have at least a list or two that can get you to the top tables with some help from the dice and matchup gods.
2. Nothing to add
3. It has become bigger. There's a format called ITC that takes in tourney scores from around the world and makes a circuit that tracks and awards performance after the las Vegas open each year. (For example I got recognized and given a sweet glass trophy for being the best
BA player worldwide last year

)
The participation in the circuit has gotten steadily and substantially larger each year, and it seems that certain online efforts like frontlinegaming, miniwargaming, and other similar sites and podcasts have been helping to grow the game's popularity.
GW itself has even come out of its shell to face the outside world on social media. History may remember this last couple years as the start of a
40k resurgence that pushes it back to the uncontested top of table wargaming.
4. Nothing to add here either.