1.- yes you can leave your vendor online, but it will not generate atoks, aslo you cant use another char on account while vendor is online, to activate, use the command @autotrade while you have shop active
2.- most seasonal headgears, have the effects of the forsaken knight helm, some of hem have different effects (like the eyepatch, cat eyes, tongue and maybe others) unfortunately there is no place to check all the items, (the item db on control panel doesn't show effects, just basic info)
3.- dont understand, u mean a npc who exchange tokens to tickets? i think no, but maybe another player knows better than me (never did halloween quests or so as player)
4.- exchange for some fashionable headgear/sell them/give to the most dangerous GM around (just kidding haha), as i said most of the headgears only have the f.knight effect.
5.- make sure it doesn't have cards and try again in the npc which is located in the elite room (for_elite 70 102)