The answer is basically yes to all your questions.
Scripts (or even just parts of scripts) can be copied and pasted within an FMP file or to another FMP file.
Whole layouts (and the objects on them) can be duplicated within an FMP file as many times as you like. The duplicate layouts can then be edited, changed and tweaked as you see fit.
Layout objects can be can be copied and pasted within an FMP file or to another FMP file. Properties, attached scripts and conditional formatting are copied along with the objects.
The only real issue with copying and pasting stuff is that, depending on the situation, you may need to edit or amend the relationships referenced by particular script steps or objects. For instance, a script will reference fields and tables within one FMP file, but if that script is imported or copied into another FMP file, then it won't work if the second FMP file doesn't have the same tables and fields that are referenced by the script. In that case, the references in the script would need to be amended to work with the tables and fields in second FMP file.