First ask is quite easy in Anaplan. Please share your example in detail will try and help
1. In order to retrieve the data need to see the dimensionality between the source module and the target module.If these are different what connects these two modules? Or do you want to get the aggregated values from the source into target module?
2. Users will Not be able to add Line items instead they can add list items. Not sure why do we want users to add line items.