1. How can I delete the preceding bars
If I enter a negative value for -x in Shift + B, only the subsequent measures will be deleted.
Should I delete them one by one?
Why aren’t “Setup” and “Write” modes displayed when in “Engrave” mode?
You can use the system track:
Press Shift+6. Edit Ctrl+6 ! Thank you @Janus for correcting me.
It’s the toggle to show/hide the tool bar.
Thanks.
Is there no value, like with a popover?
surely ctrl-6?
YEs, you can select the first note and type Shift+B, -14 for example.
Ooops 
! Thank you 
Shift-B always works from the selected point forward. With a positive number, bars are inserted, with a negative number, bars are removed.
Thanks.