I'm not a veteran ED nurse but I'd thought I'd try to answer your questions regardless of my short time in the specialty. I think it's important to consider that in the ED you won't always be taking care of trauma patients or working codes. That might be a fraction of what you do but the majority of the time you'll be working with run of the mill ED patients, some of whom should have seen their primary care doctor but for whatever reason use the ED for primary care. You'll deal with aggressive people, drug seekers, homeless people with lice and scabies who smell so bad that you might need to barf when you leave the room. That part is sad and can wear a nurse down. Also, you'll realize, if you've worked in more than one ED that EDs can vary a lot in work conditions and you need to interview wisely so you can detect a xxxx hole and stay away from it.
Some EDs have unsafe staffing, favoritism in assignments so that some of the staff always get the sickest and most work intensive assignments. Not all ED doctors are cool with nursing staff and some of them are just as degrading to nurses as they would be on general medical floors.
If you enjoy seeing a variety of patient populations and medical scenarios some of which are life threatening then the ED might be for you. If you like a fast paced enviornment where you are constantly shifting your attention and re prioritizing then you'll probably enjoy it.
Recognizing a sick patient comes with experience, you'll have to see patients to get that clinical gut of who's about to die. Your basics you learned in nursing school
will guide you to spot sick patients. Skin signs will tell you a lot about how sick a patient is. Cool, pale, diaphoretic patient should grab your attention. If a patient is worried about them self, if they think they are about to die, you should not dismiss their concern.
I've only been in the ER for a little over a year and the thing that keeps me coming back is the patients, seeing so many different people and sometimes making a profound difference in their lives. What might be the end for me is the workload and unsafe and short staffing that I have found in the last 2 EDs I've worked in.
ACLS, PALS, are requirements for most EDs, sometimes they require TNCC. Getting the CEN in my opinion before a solid 2 years of experience won't really add much to your resume and income, so I'd forgo it until you had solid skills and knowledge in the specialty. That's just my opinion about the CEN though.