How to copy a whole page?

You can create a Template or you can just save an empty score and re-use it. I do the former for brass and the latter for piano and piano-vocal parts.

Create your (empty) score just the way you like it - all boxes, text attributes, spacing etc.
Close and Save it (e.g. Drum_4lines_blank).
Write- protect the file (varies according to Operating System).

Next time you need it just open it and save under a different name. If you use it a lot then it will usually be found under File->Open Recent.

If you mean that you want several similar pages in the one file then it is easiest to create many blank pages and just delete the ones that you don't need. ([Ctlr]-[Shift]-Right Arrow followed by [Del] kills everything from the selected point to the end of the file).