Based on you description, the only missing step is to add a connection string entry in the web application's web.config file. The connection string entry must have the name of the connection string used in the report.
On configuring a SqlDataSource component
you can save a connection string by name (it will be searched in the application's configuration file), or you can hard-code the connection string (it will be the same always).
If you have a scenario where the connection string should be changed at run-time, you can switch to an ObjectDataSouce component
that allows you to use a custom data retrieval logic. The data access layer can be loaded in the Standalone Report Designer tool by extending the tool's configuration - Extending Report Designer
(tutorials at the bottom).
About using the HTML5 Viewer, please check how it works in the overview
The viewer's properties
can be configured from the VS Property grid, where the VS item template provides the viewer with some default settings.
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