Thanks for considering Aspose.
Well, in the new Aspose.Cells versions, we put some work and optimized its performance. So, if you need to apply some style formattings a whole column / row, you should use Cells.ApplyColumnStyle / ApplyRowStyle() methods which we introduced recently.
Consult the following code for you need:
Workbook wb = new Workbook();
Worksheet sheet = wb.Worksheets;
style = sheet.Cells.Columns.Style;
//Or add a new style like the following.
//style = wb.Styles[wb.Styles.Add()];
style.Custom = "#,##0";
flag = new StyleFlag();
flag.NumberFormat = true;