Mechromancer class is to be release on Oct. 16th. Golden Key from pre order is one time use per account weapons spawned out of the golden chest are based on your level at the time you open it. It is not known if there will be other ways to get golden keys. It is assumed that there will be at some point. Bank is account wide. Badass rank is account wide. No cap on ranks. You can turn the stat buffs on and off if you so chose at any time.
Only the host needs the Gamestop exclusive Creature Slaughterdome for everyone to be able to play it in a co-op game.
I can't wait. My preorder is burning up my steam account as we speak. And yes, they have confirmed you can get more golden keys, through community events and other things of the like.
Little more info on the golden loot chest. It always has purple loot and keys will only be given out at special events. The weapons and items are like any others in the game and can be traded or given to your other characters through the bank. So what that means is that it basically acts a regular chest but with out a random quality value at the time of opening. As it is only purple gear it comes down to at what level you want some purples for you characters no need to do crazy shit like waiting until all DLC has been released or something like some people over on the BL2 forums have been saying . Also something to keep in mind you won't even get to the chest until around level 20 on the first play-through and most people are going to finish the first play-through at around 30-35 so if you want to get the most out of that one key you get for the pre-order it might be best to wait until 40-45 to get the most use out of the guaranteed purples although that is not saying that the character you open it with will find a gun you want to use with them.
I will probably just open the chest right away. If this game is anything like the first, you will find plenty of blues and purple on your first playthrough, probably even a lower quality yellow. If I am going to get any use out of the guns the chest gives then I might as well go for it right away.