Thank you very much for posting your feedback.
* You can use the result of one lookup to filter another, datalookups return text however, so if you are trying to filter an id field you will need to convert to a integer(see attached).
* Data source variables are designed for when you need to return multiple properties( https://help.nintex.com/en-US/nwc/Content/Designer/DataSourceVariables.htm ( https://help.nintex.com/en-US/nwc/Content/Designer/DataSourceVariables.htm ) ). This should allow you return the information needed. We are looking at objects for data lookups as well.
* Data source variables can also deal with mutliple results, while not ideal it's possible to modify the collections and display the data in the fields using variable functions.
At this time, we will not be adding showing DSV's in repeating section to the near-term backlog, as we are focused on adding additional connector support. However, we reevaluate requests every quarter and will reach out if priorities change. Please keep the feedback coming as it is critical for our longer-term planning.