The errata adds the word "only" to the first part of the ability, now reading "when you can an instant or sorcery spell that targets only a single opponent or a single permanent this turn" instead
The expansion symbol is an eye looking through a rift portal
Even 1 damage dealt to a creature from a source with deathtouch is considered lethal damage, so any amount greater than that will cause excess damage to be dealt, even if the total amount of damage isn't greater than the opponent's creature's toughness
Due to being counterfeit products, most collector, local card shops, and investors wont touch fake products, so theres no real value there
The key differences come down to opponent count, card pool, and a handful of rules tweaks: Opponent count: Brawl is a oneonone format
If you just arent really sure if your online price checks are solid or this whole thing is just sort of overwhelming, have someone else do the work for you