Why isn't force:source:push working with Data packages defined in my sfdx-project.json?
The error arises because the Data Package contains csv files, which are not natively supported by Salesforce. In order to bypass the error, add the package path to the .forceignore file. This will not inhibit creation of Data packages.
Why is the version number for data packages have to end with zero? Doesn't it support .NEXT?
At the moment, it is not supported and we have a bug where the .NEXT is not replaced by passed build number. So ensure that all your source packages in your repository has '0' as the build number