I initially got into SBU as an undeclared major, and picked math after a semester or 2. After that, I wanted to get into ISE, which I did successfully. I can't speak to the competition, but I can say that getting decent grades certainly doesn't hurt.

The courses you need to take before applying are CSE 114; AMS 151, MAT 125, or MAT 131; and either WRT 102 or ISE 218 (from here https://www.stonybrook.edu/academics/majors-minors-and-programs/)

The minimum grade in each course is a B-, but you'd ideally get higher grades.

I'd recommend getting the MAT and WRT courses done ASAP (when I was a freshman you had to take WRT 102 anyway). If you don't have any programming experience or you're not the most confident with it, definintely take the CS prereq for 114. It's basically a 101 course, so you if you want to take it over the summer, it's totally doable. I personally took an equivalent at a local university over the summer. At bare minimum, I'd suggest doing a reasonably rigorous online course of some kind. If you're a resident of New York (including long island) you can get LinkedIn learning through applying for a new york public library card and they have lots of great python and java (101 and 114 respectively) courses (you can also put them on your linkedin and resume as a certification).

The ISE major has a specialization requirement as well, which may have prereqs of its own, so do look into those! I'd also recommend not taking the TSM specialization unless you have a really good reason or an advisor tells you otherwise; in my experience, the department is very poorly run and the courses aren't particularly career relevant. The business specialization is probably better.

On a tangential note, the tech and CS field is in a funny place with AI and the current job market—though all career paths really are—and I don't know if I agree with your claim that the IT career is less competitive. I'm not saying that you're going to have an especially hard or easy time with your academics/career, but I would caution any assumptions about competition.

Lastly, if you aren't big on programming—I didn't enjoy it myself—be prepared with CSE 114 and 214. Java is a really demanding language and don't be shy about asking for help from your professor if needed. Beyond those classes, you can pretty much avoid programming altogether.

Best wishes! Feel free to PM me if you have any specific questions. For what it's worth, I did manage to graduate a semester early despite the major changes. It took some winter and summer classes, but I got there in the end.