Starting IVs and intubation is a possibility, though it really depends where you work. At the hospital I work at, intubation is left to the respiratory techs or doctors, and IVs are started by the nurses.. unless you happen to be a phlebotomist, but that's a whole extra class and more time and money.
Do be aware that it could potentially be tough to get into an ED. Most of the EDs where I live say they require 1 year of ambulance experience or 6 months of prior ED experience (of course, it's easier to get 1 year of ambulance experience than it is to get 6 months of ED).
It is possible though - the place where I work seems to be more concerned with finding hard working people who have career goals in mind (future nurses, paramedics, doctors, etc.. rather than those content with being an EMT). But that's also part of the reason that I have to commute 20 miles to work everyday (which, in Los Angeles County, is a hell of a commute).. and work nights. The competition to get into an ED may vary depending on where you live, and the scope of practice allowed in that ED.
This is not meant to scare you in the least.. I'm just trying to give you an idea of what path to follow (by all means, apply to ERs right away.. you may get lucky) if you're planning on working as an EMT. As someone else mentioned, if you're just planning on getting a cert and not working.. then you might not even bother. The strength of being an EMT is not in the knowledge you get from the class (which is relatively limited in most areas), but the patient contact you gain from working.