I'm glad you brought up the 2v2 games. They don't happen as much as they used to, but some of the best matches I play on Thursdays are those impromptu multiplayer matches. With the influx of new people over the past month, it's certainly a more efficient way for the newer crowd to meet everyone else, while also giving players the chance to see and learn more in an evening. I'll be encouraging that.
The Trios tournament is coming up August 6, and I expect some players looking for 2v2 practice.
In that format each team of two each brings:
1,000 Point Army List (1 HQ, 1-3 Troop, 0-1 Elite, 0-1 Fast Attack, 0-1 Heavy Support)
1000 is pretty easy for most armies to write up on the fly.
An informal tradition of 1750-2000 games started with the original crew. We were playing both to have fun and to practice for the tournament scene. As we extended an open invitation for others to join us, that just became the bar for others in terms of what to expect.
The store did try to run regular Kill Team games on Saturdays, with squads of 200 points and each model acting independently (but not as Independent Characters). It went okay a couple weeks, then faded to complete nothingness. I do recall the list of necessary restrictions was absurdly long.
So in other words, you're the first person who's asked about games as small as 500.
If others are interested, they should definitely speak up!
As for tables being open, it hasn't been a serious concern to date. As full as some Thursdays get, more tables can be set up if need be. But if all those extra tables fill up...