a \new Score question

[James Bailey]

I know that doing \new Score is generally not recommended, but in the  
process of helping someone I came across a couple of questions, and  
the only solution I could find required me to do \new Score. First,  
the goal here is have a score with four separate staves, but an  
ambitus that encompasses all of them; it's a canon.
\version "2.12.3"
erster = \relative c'' { \repeat volta 4 { c d e f g2 g c,1 } }
zweiter = \relative c'' { \repeat volta 4 { c2 a h4 a g f g1 } }
dritter = \relative g' { \repeat volta 4 { g4 f2 d4 d1 e } }
vierter = \relative c' { \repeat volta 4 { c1 g2 h c1 } }
\new Score \with { \consists Ambitus_engraver } {
   <<
      \new Staff \erster
      \new Staff \zweiter
      \new Staff \dritter
      \new Staff \vierter
   >>
}
This generates almost the desired effect. I have all four staves and  
an ambitus that encompasses all of them. Problems:
• The ambitus shows up in the last system
• I get errors in my compile: "programming error: tried to get a  
translation for something that is no child of mine" six times.
• adding \layout {} or \midi {} to the \new Score results in a fatal  
error and no output is produced
• compiling with 2.13.14, the ambitus shows up below the systems,  
i.e., not on a staff, but floating below.

My questions:
• Is it possible to force the Ambitus to show up in the first system?
• Are the errors something to worry about?
• Is it possible to have \layout {} or \midi {} with \new Score {}?
• Since it's probably a bug that it worked in 2.12, should I be  
concerned with the 2.13 output?