If you exile your entire library without exiling a legendary nonland card with lesser mana value, you will randomize the exiled cards and they again become your library, ending the effect
PSA 10 graded copies would command a premium above raw card pricing
send as many cards you control as possible to the GY, except from the Extra Monster Zone, and if you do, send cards your opponent controls to the GY, up to the number of your cards sent to the GY, then, inflict 300 damage to your opponent for each of their cards sent to the GY by this effect
Many of the more powerful Counter Traps have a cost or downside to using them, however, so attempting to rely on a very large number of them may result in greatly diminished resources for the player to use
Well usually go for the rest effect, but the -1 cost-reduction can come to use
All in all, trading and collecting is really exciting and fun to do in your free time