Welcome to the forum, remelvert94. For your first issue, I guess you just created a super-long bar because you didn’t know how long it was going to be in advance? Now you’ve put the music in, you could try creating an asdditional barline at the start of all of the surplus space, then do Shift+B to open the bars popover, and finally type -1 to delete the bar containing all of the surplus space.
You can’t cue a whole percussion kit, I’m afraid. You could add an extra player to your project using a pitched staff and copy the material to be cued to that staff, then hide it from the full score layout and use it just as a source for the cue. It will look right in the destination staff, but won’t actually be the material from the percussion staff.