Which SQL Server license is appropriate for my use case? Can I use a free license?
Free Edtions
SQL Server 20xx Express Editions
SQL Server 2019 Express Edition is free for production, non-production, and redistribution.  After install you'll find the license terms at
C:\Program Files\Microsoft SQL Server\150\License Terms\SQLServer2019_License_EXPR_1033.rtf
SQL Server 20xx Developer Editions
If you install the free SQL Server 2019 Developer Edition, you'll find the license terms at
C:\Program Files\Microsoft SQL Server\150\License Terms\SQLServer2019_License_DEV_1033.rtf
Which reads in relevant part:

Non-free Editions
For for the non-free editions of SQL Server refer to the licensing guide here.
You can also run these editions of SQL Server for non-production purposes if you have an appropriate Visual Studio Subscription (formerly called MSDN).