Can you tell us more about the logic that you think can't be done in a data entity? Note that you can write X++ code in entities, therefore you can put any arbitrary logic there, while you don't have to reinvent a framework for data import.
The point is they want to import some dynamics fields in sales order form as well which is not present in the sales table which can't be possible through data entity so we need to create a class for this.
So when user import the excel it should automatically create fields in the table which is present in the excel.
So before that I need to create a simple import utility for sales order.
Are you 100% sure that you can't use Data Management and you need to invest a lot of time to designing, developing, testing and maintaining a custom solution?