Do I need a database license for my application? I am developing an application for cemetery management. It is my first "big" project, so I'm not familiar with the "corporative" side of this.

First, some info about the app:


Has 3 local database files, one for authorizations (Login and permission purposes), another for option storing (each of these two has only one table) and another for the system itself (this is the main one, and has 5 tables).
In general, the system stores all the info of a small cemetery. This info includes deceased, graves and payments (3 tables). The other 2 tables are one for crossed information and another for vacant graves.
There's storing and retrieval of info between the C# GUI and the SQL.
The application is for academic purposes for now, but it may be a serious thing in the future (own business maybe?), so I'm a little worried about legal problems with M$ in the future.


Main Question: Do I need to pay for a license? Either for SQL or Visual Studio or anything else.
It does not sound like your database and application would be very big in current terms. 

You could look into the freely available Microsoft tools for Visual Studio Express and SQL Server Express:

https://www.visualstudio.com/en-us/products/visual-studio-express-vs.aspx

http://www.microsoft.com/en-us/server-cloud/products/sql-server-editions/sql-server-express.aspx

Both of these are without charge and contain most features of the bigger products.  The limit is in database size, amount of memory, and number of processors that can be used.