Apart from what ever has been answered it is a good practice to catch the general exception also. In both the catch blocks you have to do 2 things log an exception as well as Display the exception to the user. But my suggestion is if you can avoid exceptions that would be even better so have proper checks where ever required like null check etc etc.

If you are already using ADO.net I wouldn't suggest you to go with EF. If you wish to use EF you can use it You can even use your existing stored procedures if you want but may have to do some changes. The decision with EF or ADO.net depends on other factors also like 1) if you want better performance and working on huge data then go with ADO.net. 2) Whatever you are comfortable with. If you have a very good expertise in ADO.net then go with ADO.net or if you have very good expertise in EF then go with EF. Instead of a 3-tier architecture I would suggest you to try GUI Architectural patterns either MVVM or MVC depending on the type of the application. If you want to use 3 tier architecture then there may be more layers required to have separation of concerns e.g:- for cross cutting concerns etc.

https://msdn.microsoft.com/en-us/library/ms754130%28v=vs.110%29.aspx[^]

Just try to understand MVVM rather than going through some code. Once you can understand MVVM, You will get to know how to do that.

Have you tried the writing to excel using the interop and you are connecting using MySQL odbc. is your db really sql server?

please can you tell us what have you tried and where you are stuck?

Nice to here that your software has got awards and ratings but awards and ratings are not enough to sell a software. It should have the facts in numbers of how it will help and get a ROI .Why will people invest in your software if they don't how it will help them and if they don't know what's the ROI they will be getting from the investment. You also need to showcase how your software is unique when compared to other software.

Costing a software product is also based on strategy. You can send it for lesser price at the beginning. So that more users can use your software and once the user base grows you can increase the price. You can read a case study and get some idea from it.

If your software is really good then you don't have worry about selling it. You need to focus on marketing. “Doing business without advertising is like winking at a girl in the dark. You know what you are doing but nobody else does.” ― Steuart Henderson Britt, Marketing Management and Administrative Action The product should be showcased and if it's worth then people will contact you. All you have to prove is how your product is value added to the business and provides a definite ROI.

Implementing a programming language Hmmmmmm I only worried these days about mastering one :)

Absolutely correct. We are living in a world where phones are getting smarter and people are getting dumb ;P