Hi, I am trying to save the formatting of the Cover page (name, title, date, instrumentation) in order to use it across my pieces but it seems one can only export master sets that accommodate music?
Yes, you can export the master page set containing the cover page as a .doricolib file, then import that set into other projects. You can either apply the set as a whole to layouts in the new project, or import individual pages from the imported set into the existing sets in the project.
indeed I can import the master page to new projects but it seems that the size of the text frames differ from the original (the one I made as a template) and the one that is imported. Is there any fix on this?
That sounds like frames you want to have a specific size had all four frame constraints locked. That means their size adjusts correspondingly to the page size on which the master page is used, i.e. appearing bigger on an A3 page than an A4 page, and possibly offset relative to where they were drawn as well. Here is more information about frame constraints.
If you want frames to have a fixed height, unlock either the top or bottom. If you want frames to have a fixed width, unlock either the left or right. Unlock bottom and right, for example, to fix both height and width, and the top/left sides of the frame relative to the page.
If Dorico could save the margins as percentages of page dimensions, that would be very great. For now I have to keep basically the same masterpages for each score size.