UMN admits to colleges rather than majors. To declare a major within CSE you’d need to make sure you satisfy the particular GPA requirements and prerequisite courses. Some majors may limit the numbers admitted - not sure. Best to check with CSE on that. But in general, yes, you don’t have to worry about declaring a major right away and can change your mind on what you want to study once you’ve had some college experience (many do this).
You should definitely apply by the Nov. 1st priority deadline if you want to be considered for merit aid.
Regarding admission, it’s driven by stats and coursework more than EC’s or legacy. Your ACT is obviously fine for CSE. Your uw GPA also seems fine; however, your uw class rank is a tad low. Nonetheless, CSE is most likely a match given your stats overall and your coursework. Someone on this thread last year got into CSE with the same ACT score but lower class rank so you should be fine. Subject tests not required, though if you submit them they will be considered as secondary admission factors. Don’t wait on these before applying!
Here are the latest admission stats by college:
https://admissions.tc.umn.edu/academics/profile.html
The most common types of merit aid include both university-wide scholarships and college-specific scholarships. For university-wide, the biggest scholarships for OOS historically have been the Gold National (covering 100% of the OOS portion) and National Excellence (covering 50%). However, this year these scholarships are just listed as “Amount Varies” so not sure what’s going on there - could have something to do wth the recently-approved OOS tuition increases, which are markedly more significant than they used to be. Perhaps the scholarships no longer cover as much of the OOS difference as they used to.
Here is the link to scholarship information:
https://admissions.tc.umn.edu/costsaid/scholarships.html
Good luck!