I don't have experience with that specific company (EMSS), but I have been an ER scribe for CEP for the past ~1.75 years.
In terms of becoming a scribe, I'd recommend demonstrating a desire to go into medicine. As with most pre-med communities, they'll want to see you have a desire to learn the complexities of medicine, have a healthy interest in science, and general desire to help people. This is of course in addition to being a hardworker and good at multitasking. Most of the scribes will tell you the ER can be very fast paced. In our company, we do the physician's charting, which is what I imagine you have already knew. However in addition to charting, we keep track of labs, keep track of interventions (stuff we do for the patient in the ED), do patient updates, and relay messages from physicians to techs and nurses. Scribes will often have to delay their lunch (if they even take one), and there are never any real 'breaks' (see addendum). To prepare for the interview, maybe try to demonstrate a basic understanding of what you'll be getting into. Understand that you will be taking care of patients with limited history (very little background), know that some of them will be in critical condition (it's an emergency room), and working there can be pretty fast paced and chaotic. A good question to ask in the interview is what your relationship with the physician will be. Some places have scribes work for all the docs, and other places have a 1:1 scribe to doc relationship where the scribe is trained to work with one doctor and only that doctor. Some places have scribes interact less with docs than others.
And of course I'm sure you're aware of the benefits of scribing (patient contact, talk to docs). However, I'll elaborate on what I took away from scribing. Honestly, the first one I can think of is my improved ability to communicate. I am a quiet person (have always been). However, in ED you're forced to come out of your shell. Not many awkward people make it to become a scribe, so if you are try to demonstrate you care about people and/or are trying to improve your ability to communicate. Talking to patients, nurses, and docs was somewhat overwhelming at first, but you figure it out. It's a great place to start developing your bedside manner, asking questions for the review of systems. I got to ask docs directly or indirectly about their thought processes (their differential diagnosis).
That transitions to my second takeaway from scribing - seeing into the medical decision making thought process. Their differential diagnosis is like a hypothesis (if you didn't know) which they run labs and imaging to test if the hypothesis holds. It demystified the logic behind their diagnosis for me (I hadn't really had too much exposure to docs before or watch any TV lol). Also, you get to see ER docs coordinating placement of patient with other physicians/facilities, considering the feelings/needs of family members in decision making, considering patient history, etc. It really is a multi-component system that's pretty complex. Fascinating, sometimes frustrating, but very necessary. Very good insight into what you're getting into. And a good reminder that you don't work in a total vacuum in medicine.
Those were my main insights from scribing. The only other one worth mentioning is the teamwork aspect of ER medicine (and possibly most other specialities). You work with nurses, techs, hospitalists, specialty surgeons, general surgeons, radiologists, paramedics, sheriffs, etc. You're constantly trading ideas and working together to get the patient to where they need to be. Inspiring and rewarding stuff, especially when you're slammed with patients or getting really critical patients IMO.
ADDENDUM : It's fast paced, but on some shifts there is 'downtime' where you can shoot the **** with the ER physicians, look at your e-mail, or surf the web. I would say 'no' to social media, but I have seen physicians and nurses 'goofing off''. So don't worry so much about ER scribing being too overwhelming. It depends all on the ebb and flow of patients. Also depends on what shifts you work (days, nights, holidays).
Anecdotal tidbit: the ER docs that I worked with are almost all really 'chill' despite, or rather because of, the stresses of the ER. And in my experience, they're all really down to earth. They hear firsthand what it's like having no insurance, coming from broken/nonexistent families, or having very few resources. So don't stress out too much, it's a great place to start to talk to docs because they're so approachable and understanding.