Multivariable calculus is usually considered easier than gen calc. The subject matter may be more complex (calc in 3-dimensions) but the actual calculus (integration) tends to be a lot easier. If you found that you were pretty good at calculus, this course won’t be an issue.
Organic chemistry is really challenging. If you already took some orgo in highschool, that will help a lot. It boils down to a ton of memorization.
I took both of these courses my first semester and bombed both of them. Stemmed from a lack of time management/study skills and being totally unprepared for how challenging they were going to be. That said, other freshman I knew took them both and did fine.
The great thing about the advanced Orgo class is that it has (or at least, had) an extended “drop date” that surpasses the first exam. Meaning, you can take the first orgo exam, see how you do, and still choose to drop the class with no consequence (disappears from your transcript forever). Pretty much no other course has this option. It’s designed to make sure freshman don’t get in over their head; if you do poorly on the first exam, it suggests you’ve already fallen behind, and that will just compound on each subsequent exam. Naturally I did poorly on the first exam and just kept going… Not sure if this it still a policy they have in place.
By the way, “advanced placement” Organic Chem is just called that because all the students are freshman and have AP credit. It’s not more advanced than the other OChem course.
It’s hard to say what you “should” do. There is certainly no rush to take either of these courses, but it doesn’t hurt to get them out of the way before you dig into the core of ChemE. If you’re confident in your study skills, I think you should go ahead an enroll in both without worrying, but be prepared to hit the ground running. If you breezed through highschool without having to put much effort into studying at all, you might want to delay Orgo until your sophomore year.