I was in a very similar situation as you, so I thought I'd share my experience. I was an attorney before going to nursing school, so I had a prior demanding career, and I was in my 30s. I had no healthcare experience prior to starting nursing school. I did a 15 month accelerated BSN (ABSN) program. I think as a second career student, we have an advantage in terms of disciplined study time, but I found it to be a big transition to understand how to think like a nurse. It was just so foreign from what I had done previously in my life, even though my prior job was almost all critical thinking, the context was just so different. Not to mention the content that we were learning was all new to me. I think it would be really hard to do a direct entry program and not give yourself time to absorb the information and develop the "6th sense" that you need in nursing. Plus financially it's better to get your BSN and then work while getting your NP degree.
As for your experience in different areas in nursing school and knowing what you want to do as an NP, I think it's unlikely that clinical will help you much. Most of your clinical time will be spent doing adult med/surg. There are tons of areas out there that you will never see as a student. I think the best thing you can do while in school is try to decide if you like working with adults or kids or both. And then try to get some ICU time to see if you like critical care. The ED and ICUs will give you the most exposure to a wide variety of conditions. If you don't like critical care, then try to find a floor that gets a wide variety of patients. I think you learn the most and the fastest in the ED or ICU, so that would be my recommendation. No matter where else you go, that knowledge will help you.
Let me explain what I mean a little better about why the ICU gives you better experience (and I assume the ED would be similar but I don't work there). When I worked on the floor, we had very little contact with the MDs or NPs. So what I was learning was from the other nurses I worked with. Which is fine if you are just focused on bedside nursing, but if you're trying to figure out what an NP does and if you'd like their job, it doesn't help you. When the MDs rounded on the floor, the extent of my conversation with them (if I talked to them at all) consisted of "Any changes today?" I rarely focused on lab results (many patients didn't have daily labs), almost never looked at the actual x-rays or CT scans, I only read the radiologist's report.
Whereas, in the ICU, we present rounds everyday to our MDs and NPs. We are expected to know and understand our patient's disease or injuries, have looked at our x-ray, know if our breathing tube is in the right place, know if our feeding tube is gastric or transpyloric, and also read the radiologist's report to know if there is anything to mention in rounds. If our patient is on steroids, but doesn't have any GI prophylaxis ordered, we bring that up. We calculate the maintenance fluid rates the patient should be getting and bring it up if they are getting too much or too little. If they are on formula feeds, we calculate how many calories they are getting. We talk about their sedation and pain medication, and if they are getting too much or too little. Almost all of our patients have at least daily labs so we talk about all of the labs and discuss any abnormals, why we think they are abnormal (if we know) and what we might be able to do about it. We analyze our blood gasses and think about if our ventilator settings are adequate, or is the patient alkalotic due to diuretics, and it isn't a respiratory issue at all. In sum, we look at everything about our patient, and think about every system for every patient. It is a completely different level of thought than what is required on the floor. And it is exactly what any NP needs to be thinking about for their patients (at least any inpatient NP).
Primary care is very different, but none of this knowledge would hurt. It is so helpful when you're in NP school, and you're already used to thinking in this way. Also in the ICU, you get to work with more areas in the hospital, so you can get a better feel for what the other areas do. You spend time in MRI and CT, you get patients from the ED, send and receive patients from the OR, and send and receive patients from the floors. You generally get a lot more exposure to different stuff.
I did what it sounds like you're thinking of doing. I did an ABSN, got a job and then applied for NP school. I've done school part-time while continuing to work full-time. I will have 3 1/2 years of full-time nursing experience when I graduate from NP school. I feel that this has worked out really well. I've had enough time to learn what I need to get by and do well in my program. Another 5 years of bedside experience would be nice, but definitely not essential for success. However, any less experience and I think I'd be really struggling to get through school. I still struggle to remember everything, and more bedside experience would probably make this easier, but I can manage ok without it. But without my bedside experience, there's no way I'd be able to remember all of the drugs, all of the diseases and all of the labs that I should know.
As an older student who had good grades in my ABSN program, and who knows how to write a good cover letter and resume, I did not have any difficulty getting a job. In fact, when I graduated the job market was worse than it is now, I got the first job I applied for and it was a highly competitive residency position. It may take a little networking, but I'm sure you can get into the specialty you want when you're done with school.
Sorry this got to be so long! I hope it's helpful as you consider your career change. I know switching to nursing was the absolute best thing I've done in my life. Good luck to you