1) hode reduced all earth damage attacks (Ad gets false endowed by the weapon) so yes it helps vs djinn bios, might not help that much vs profs though as they have pretty much every element to their disposal.
2)We don't have and Odin's cards D:, you can create elemental resist pots though, I'm sure there is a guide on the forums.
3) never heard of Tengo?:/ And it's not on RMS or Roempire.