Excel migration to C# application

[bigN]

I didn't know where to post this question, but this was as close as I could get.
I have an excel application which I want to transfer to winform C#.
Brief Description of Application
1.) In my application I have several Sheets A,B,C etc (normally 40-50sheets) where I put my data.
2) After, I copy the data to A(1),B(1),C(1) (another 40-50sheets) and make my calculation via VBA, deleting, adding rows etc. until I get the required results.
Sometimes, I create another copy of A eg. A(2) and start calculation again and after comparing the results of A(1) and A(2), I delete the unused version.
3) After I am satisfied with the result I make the reports of A(1),B(1),C(1) via Pivot tables.
Questions
) What is best way to simulate the Excel sheet in C# app eg. dataset, datatable, IList, since I have a lot of sheets (more than 100 per project)?
2) What database should I use (Access, XML, SQL) to store the data sheets of A,B,C and A(1),B(1),C(1) the application will be used Locally only?
3) My main question is, how should I solve this problem in theory, a pattern or perhaps a process description from experts would be really helpful :).
I hope this makes sense....