I'll tackle each of these one by one.
1. Foul Play doesn't actually do anything to any of your opponent's Pokemon until you have chosen an attack to copy and carry that attack out. That said, if you copy an attack that has effects other than damage, Espeon's Solar Revelation would stop those effect, though the damage would still be processes. Foul Play simply lets you choose one of your opponent's Active Pokemon's attacks, but it doesn't have any effects on your opponent's Pokemon on its own.
2. Dangerous Energy does stack. If you had multiple attached to one of your Dark Pokemon and it was attacked by a Pokemon-EX, you would place two damage counters on the attacking Pokemon for each Dangerous Energy attached. Typically, effects stack unless something specifically stes that it doesn't.
3. Pokemon Tools cannot be switched freely. Once a Pokemon Tool is attached to a Pokemon, it remains on that Pokemon unless an effect removes it, such as Xerosic or Startling Megaphone. You can't simply discard a Pokemon Tool because you want to attack a different once. If you look at the text of a Pokemon Tool Card, it will say something like "Attach this card to one of your Pokemon that doesn't already have a Pokemon Tool attached to it" (In that case of Team Flare Hyper Gear it's one of your opponent's Pokemon, but the same rule applies. Once a Pokemon Tool has been attached, it's essentially thee as long as the Pokemon remains in play, so think carefully before you play your tools!
