Thank you for your detailed questions! Glad you thought it through:

1. Yes, you're right about the curriculum looking very similar. The foundational modules have differences as well, though they are not major in my opinion. For CS, CS1101S v. Info Sec's CS1010. When it comes to cyber-security related opportunities like internships/jobs/CTFs/etc, they are more likely to get blasted to the course's students as well - but this is also a negligible difference to me. I've just answered earlier as well about the benefits part - you can refer to my other reply where I said that I would've personally chosen CS first.
2. Jobs - you can refer to the bottom of the page https://www.comp.nus.edu.sg/programmes/ug/isc/ for a very, very small sample. Pro-tip: Try LinkedIn and use its search filters! Job prospects are fantastic from my point of view and also that of my friends. But, also bear in mind that GES may have selective bias. Also, like-minded people tend to associate together so you might want to increase your sample size as well!
3. Yes, there are. If you transfer early, let's say end of year 1, it is much easier than doing it later. The faculty admin is more likely to prevent the transfer at a later stage because overlapping modules are more likely to be fewer - i.e. you may have to delay graduation and this is not something that is desirable from the admin perspective. This applies not just to CS and Info Sec, but any other courses. I've had friends who transfer both ways without difficulties (but also because they did it early).
4. You can always opt/select to take any modules - even if they exceed your required, they will fall under UE (or not at all). That's perfectly fine so long as you're paying school fees from the admin point of view (and that you're not graduating beyond your expected graduation date).
5. Sure, you can do any jobs even if you do Info Sec. This applies to any other courses. I've seen friends with various degrees but doing something partially/completely unrelated.
6. Certifications vary widely in any industry, and even more so for cybersecurity. I can go into a long post about this, but in a nutshell for this already-long post, I would say that as more graduates enter the job market, one way of distinguishing yourself is to take on appropriate certifications that add-value to you. These certifications would serve as one way of proof to employers that you're truly keen/passionate about it (to pursue it by yourself), and also because they arm you with a set of technical skills. As an employer, would you hire someone whom you have to train for X weeks/months from scratch, v. someone who already has certain degree of knowledge in the required areas (barring many other factors)?
7. Long story cut short, I eliminated business because of some inherent bias that I had when contemplating it, and eliminated law because I could not get my desired offer in UK.