1) 350 members online at one time is pretty good. We currently hover over 200, in the past it used to hover around 100.
2) pretty much every website has more visitors than members. I browse IGN and other videogame websites, but this is the only one I'm a member and actually log in for. (I'm a member at gamefaqs so I could gain some information, and haven't logged in since )
3) quick links -> VGChartz IM. You can get to it from every single page. In fact, it is easier to get to than the sales charts.