Congrats for acceptance and scholarship
Both schools are fairly close to each other from a ranking view. Both enjoy small class size. ND is smaller though. Despite difficulties for any international that exist in any school, the career service in Olin is doing great job while ND's alumni is great source of opportunities. In my opinion, if it concerns you, there is huge difference in the diversity of courses. Olin has wider electives to to study. ND is somehow limited compared to Olin.
I do not know exactly but I think ND is cheaper than St Louis or maybe too close.
Something interesting for some people is the balance among case method, lecture and experiential learning.
I think you should contact current students to know more.
How do you define the culture fit?