Oh boy.
There are over 3000 applications for 110 seats last year ...
That's below average. But the point of the exercise was to see if there's a fast "yes" answer to "is your one and only school WAY too competitive for this plan?" And the answer is no. Which leaves harder questions.
I think I am more concerned about residency and fellowship since I am also limited to that one school. I want to be a cardiologist but would certainly apply for other specialties. How difficult that is going to be?
This says you don't know how residency works. Which is fine, but as a nurse you should have access to doctors, preferably fresh ones, and you should be using them as mentors. You need a sense of proportion, and perspective, and prioritization for your concerns.
Cardiology is about 6 years of training after 4 years in med school. You can't specialize in cardiology out of med school. You go after internal medicine, which is what probably 50 of those 110 students match into each year. It's the default specialty for med students who can't decide what they want to do. There are more residency seats in IM than in all but one other specialty (family med). You have to work pretty hard to not match IM. Point being there is absolutely no concern about getting an internal medicine residency, in terms of whether any one med school is competitive, all else being equal (which it's not: you have to get through med school and have good board scores, regardless). If you want to be fantastically prematurely obsessed with whether you can get into the "right" IM residency to position yourself for cardiology fellowship, with no MCAT score in hand, take that over to pre-allo where rampant speculation based on nothing is the whole point of the subforum.
In other words, it's completely out of proportion to be worrying about residency and fellowship at this point. That's a hurdle after these hurdles:
1. Get the med school prereqs done with better than 3.6 (med school prereqs are generally not the same, and are generally harder, than nursing science). Very difficult because the med school prereqs are a graveyard of champions.
2. Get a good MCAT score. Another graveyard of champions.
3. Don't blow your marriage. Seriously.
4. Somehow get accepted with only one school on your list. Very low odds.
5. Survive the first 2 years of med school. This is the 2nd most miserable part of medical training for most people. (Most miserable, typically: intern year of residency.)
6. Get a good Step 1 score. Another graveyard of champions.
7. Do much better than just surviving 3rd year. Fun fact: you don't get honors in 3rd year rotations without having already been at the top of your class.
8. Get a good Step 2 score. A slightly less spooky graveyard.
I just don't want to find out about that after four years and 200K in debt.
That's a good thing to be worried about, but again, what's more critically at stake is the following stereotypical problems:
1. Can't get A's in the prereqs
2. After all the work of the prereqs, can't get a good MCAT score
3. After all the work of the prereqs & MCAT, can't get an acceptance
4. After all the work of getting in, can't survive 1st semester anatomy
5. After all the work of surviving 1st & 2nd year, blow Step 1
$200k is a low estimate. If you will be borrowing cost of attendance, $250k is the current average. And rising.
Clearly you're trying to be pragmatic and make a very solid decision to do right by your family. But you aren't up to speed on the issues that would let you
actually be pragmatic and make a solid decision. I would expect that you will find the pragmatic, solid decision is "nope". You can get to nope without doing the work to understand what you're getting into with med school, or you can do the work. Your gut reaction to being told "give up now" is also good information.
Nobody is going to be able to give you a valid answer to "should I even be considering this?" You are in an SDN subforum that is full-to-busting with commentary from people who have tried to do what you want to do. There are a bazillion parents, nurses, and location-bound former premeds here on SDN, if you choose to do the work to research this extremely difficult, expensive and lengthy career change.
Best of luck to you.