It's an artifact, and plenty of cards care about artifacts entering, leaving, or being on the battlefield
A: To answer your other questions literally, there is nothing on Dream-Gate that would prevent you from playing Read the Signs and then Practice Makes Perfect to investigate there, at Dream-Gate
Starting at three mana makes it easy to consistently cast her on turns one and two every game, and having four toughness means you wont have to re-cast her as often, as her backside is big enough to not be bothered by Bolt or Bowmasters for the most part
A Fire-type deck will generally lean towards expensive yet lethal damage, for example, but Lightning-type decks can suit a myriad of player types
Tom Bombadil, for example, would love this card in Commander since it can create a copy of your Commander