You are right that EM people tend to be very cool folks, a little nuts, laid back, and a fun group. It's a culture thing, one that I'm very fond of.
As far as the multitasking goes, Roja is right. It's a personality thing, but also a learned skill. Take the perspective of the consulting physician who comes down to the ER to admit a patient. Not knowing what is going on, the ER seems loud, hectic, and disorganized. It's a wonder that any kind of medicine is practiced at all down here. From the ER doc's perspective, though, things are going just fine. They know about each patient, having an idea about where each one is going and what is still pending.
A mass casualty incident looks pretty hairy from the perspective of the paramedic, but not so much to the incident commander, who has the larger view of the situation. The ER doc has honed his clinical skills to the point where a lot of the patient care is pattern recognition and reflex. He's not agonizing over the clinical decisions, as they come more easily through experience and training.
As your knowledge and clinical skills grow, you will be able to take a larger and larger view of the department, able to deliver good patient care and manage department flow at the same time. It's easy to be overwhelmed by your first chest pain patient that you've had to manage yourself. After seeing several hundred of them, it requires less effort to see all the different directions a chest pain workup can go. There's a reason that ER docs are so cool running a code and vascular surgeons are so cool with a spurting vessel. They know that if the worst possible thing happens, they can handle it. There is therefore not so much stress.
As a side note, it's okay to enter medical school with an idea about a career that might appeal to you, but there are many specialties out there that you may not have been exposed to that may be an even better match for you. You may find that surgery or opthamology or internal medicine is what really lights your fire. Don't let your envisioned specialty dictate if, how, or where you go to med school.
'zilla