How to selectively import and export specific content without overriding existing destination database?
As you already mentioned, use features module to transfer configuration. 

For actual content, you will need to use Views Data Export to export stuff. Make a CSV file. 

VDE tutorial

Then use Feeds module to import the CSV file content into your other site.

Feeds Tutorial

Alternatively, for nodes you could just use Node Export, but you will still need feeds for the taxonomy importing.