Iron banner will return on Tuesday. And yes, you can get to 4OO without raising, I did it with strike hoard chests, faction packages, exotic engrams, archons forge, and iron banner. As well as a little bit of nightfall strikes and a couple normal crucible matches.

Don't know about IB date. 400 can be done without raids. I had all three characters at 400 before making a run in WotM. It was a grind, but not all THAT difficult. IB will be good for high light equipment. Archon's Forge will drop high light items also. Once you get up over 385, pay attention to the blue items that drop in the Forge. I've had quite a few very nice blues that I was able to infuse into Legendary and Exotic pieces.

400 light is max and can be acquired without raiding. Also if it helps you at all, before I bought Destiny I never ever wanted to talk to anyone while playing a game. Partially for the same reason. I also thought they'd all be children and it would be wierd. Much to my dismay this was not the case and I've met some very awesome people in Destiny. This game is fully realized when you've found a like minded group of people to do end game content. Now every other game is boring.