Thanks for your request.
1. The best way to insert a form field is using DocumentBuilder. Please follow the link for more information:
2. Please follow the link to learn how to create comments using Aspose.Words:
If you need to associate comment with a selected range, you should use CommentRangeStart and CommentRangeEnd nodes to mark the selected range.
3. Actually there is no column concept in MS Word tables. By Microsoft Word design, rows in a table in a Microsoft Word document are completely independent. It means each row can have any number of cells of any width. However, you can suppose then number of cells in the first row of the table is a number of columns in the table.