Hey! I am from SP DACP-Applied Chem With Pharma Sciences.
So here is some of my thoughts!
To begin with, NUS Chem structure. Year 1 and 2 are basically foundation years. In these two years, you will be dealing with tons of Chemistry core modules such as Inorganic, Organic, Physical, Analytical and on top of that, you have your lab modules which aims to drill your laboratory skills while at the same time, expose you to different analytical equipments!
IMO, year 1 and 2 is pretty similar to DACP, except this time we are compressing a few semesters worth of work into a few hours of lectures. I am not sure about perfumery diploma tho. You might want to compare and contrast SP's syllabus with NUS Chemistry syllabus! This can be found easily by running a Google search!
Next up, moving on to perfumery. To my extent of my knowledge, I believe perfumery is a subset of organic chemistry! So if you are into synthesizing and extracting compounds to create these perfumes then yes, nus chemistry can be a great starting point! However, do take note that NUS does not offer perfumery related electives in the department of Chemistry! So this might pose as a problem if you want to learn how to smell and formulate the perfume. (You might want to go for the open houses next year or so [if you are going for NS] to ask if there are other perfumery related electives out there!)
Whereas for competition, here is my word of advice. Do not fear the competition. Treat it as a driving force to motivate yourself to do better!