measures per line

Not.
Line breaks are considered content (or at the very least dependent on measure content) and as such are not maintained when starting a new score from a template.

If this is very important to you, you can always load an existing empty score and use "Save As.." to save it. (Or borrow from the daily log plugin to partially automate such a thing).

But probably better to just run Format / Add/Remove System Breaks immediately upon creating the score. In most cases it isn't really necessary or helpful and can be counterproductive because normally you don't know until the music is entered how many measures will actually fit, and MuseScore handles all that automatically anyhow. But if you're creating a lead sheet or writing music for children in which you know before you start you will definitely want four measures per line or whatever, this will do the trick easily.