1. You do need specific weapons once in a time, but my suggestion is, use the strongest weapon you have, with neutral element, (the one with no elemental strikes) cos when you attack elemental eater fiends they'll recover hp, got it ?
2. No, i don't think you can undo the costumization
3. If you press the button to a blitzer that is free, then you'll be able to contract them. You just haven't found the luck to meet a free player, just keep on trying <img src="/images/graemlins/smile.gif" alt="" />