1. Bombardment cannot happen if the final boss is defeated (although you also won't get the quest to fight the old one).
2. Cast book of absorption on the tile you want to remove it from.
3. No. Also no (although their spawn range is large, they will appear in any water in that range, hence why there appear to be more if there's little water as they all have to crowd in that small area).
4. Any smaller, and you probably wouldn't even know what it was. It's a thick cable, but I think that's ok.