I'm a New Grad at a teaching hospital and level 1 trauma center. We are also cross trained in both the adult and pediatric ERs. I think that starting out in the ER is great, but you need to be in the right ER and you have to go in with the right mindset. The ER you start in should have a solid new grad program (from my experience and what I've read, about 4 months with consistent preceptors), and preferably be a hospital that has a culture that accepts new people/students/etc. If you can find a hospital and program like that, then you will find your transition so much easier.
As far as the right mindset to thrive as a new nurse you need to be a self starter, be quick on your toes, and also be okay with man/womaning up and admitting when you need help or don't know your head from your tail. Some people might disagree with me, but I don't think that the ER is a good place to start if you insist on having a "fake it until you make it" attitude. Especially starting out, you need to be mature enough and wise enough to admit when you need help or are overwhelmed, since the flow of the unit and also patient status can change so rapidly in the ER.
In short, if you're up for the challenge and find a place that is a good fit for you, do it!!
Good luck with everything, and I hope to read about your success as an ER nurse in the future!