Hi Lara,
> I am trying to print my Web map through one of the templates available on Portal for ArcGIS. I also experience the same legend problem when i build an app with Web Appbuilder.
It's not clear to me what is causing the issue from the documentation you posted. Can you please capture the JSON communication in the web browser when you attempt to generate a print layout from Web AppBuilder? You can use something like FireBug in FireFox, Fiddler, etc.
> ... how to get the Print on the Portal for ArcGIS map viewer to behave the same way my print service behaves (with page layouts and all, i.e. Landscape, Portrait, jpeg, pdf, etc)
Enabling custom print layouts in the Portal for ArcGIS map viewer is currently not supported. This enhancement is under consideration for a future release. Please add your vote and comment on this idea on Ideas.ArcGIS.com:
Hope this helps,