How would having a Bachelor's degree affect a college application?

I'm a 17 year old from New Zealand, and have some thoughts of attempting to go to an Ivy league school or Oxbridge.

I'm in my final year of high school, but have also been taking classes at university simultaneously and will be getting my Bachelor's degree (major in maths and a minor in statistics) at the end of the year (at around the same time as when I graduate high school). How would having a bachelor's degree affect my application? Would I be a stand-out applicant considering my achievement or would I be disadvantaged for already attaining a Bachelor's degree.

Will there be many scholarships/financial aid available to international students like me? I see the tuition fees in US/UK and they'll probably be unaffordable if I don't get a scholarship (I don't want to go into student debt).

I'm currently intending to pursue a 1-year postgraduate course in New Zealand as Bachelor's degree here are only a 3 year course. After finishing this, I'm considering either going back to undergrad or applying to postgrad but if I do end up applying to undergrad I will be applying 1 year after I graduate high school. Will there be any disadvantage of applying to an undergrad course a year after finishing high school?