Kinda late, but let me chime in.
1.) No, you are at a disadvantage. In fact, due to you being an Asian, an over-represented minority in US colleges, you will face even harder competition because you are EXPECTED to do at least as well as other Asian kids. I know it sounds unfair, but that’s how US college admission works. Particularly, if you can’t afford the cost and need significant amount of financial aid, you are at even more disadvantage. That being said, if you can pay at least 25k(for less expensive ones) or 30~35k(at more expensive ones, like 65k per year) your chances are as good as those of full pay international students.
2.) Art Portfolio will be particularly interesting in your case since you are an Asian with prospective science major(again, over represented) who also have passion in non-science major. Not saying it gives a huge advantage, but it certainly gives another aspect of your personality.
3.) Again, the admission officers are NOT art experts. Sure, some professors who teach arts may look at it, but they won’t critic your works like the real critics do to many artists.
Worth applying to top colleges? It depends. If your GPA is pretty good, say at least 3.8 UW GPA and 4.2 weighted GPA, it’s certainly not bad(assuming your have decent SAT/ACT score, say 2200+ or 33+) Try ACT, it’s much better for non-native speakers, although it really depends.
4.) There are so many threads in CC that help you through SAT/ACT or other tests.
What is your current visa status? Are you under 18? Just let you know, you won’t be penalized for being here illegally if you are under 18.
PM me if you have a question. I am also a foreign student who’s a college freshman.
Good luck