Is it sensible to use the apa6 class for a thesis (with chapters)?

The comments to the question were very useful, and this advice from cfr was good:

I would not recommend using any class designed to typeset single articles for managing a thesis. You will need to change far too much. It is not just adding \chapter{} commands, things like the ToC, bibliography etc. will all be wrong. Better to figure out which few things apa6 does which you actually want and are applicable to a thesis.

Also StrongBad pointed out that the APA doesn't even have full formatting guidelines for a dissertation, so to my mind the best way to proceed is by using biblatex-apa and memoir or KOMA-Script. I went with memoir simply because the English documentation is more thorough.

From there I will configure the few necessary APA formatting things (line spacing, margins) and let biblatex-apa handle the bibliography. biblatex-apa with biber appears to provide the best APA referencing possibilities (if you want 6th style), as it allows for UTF-8 and has extra fields which make APA referencing much more pleasant for rare reference types.

Blockquotes look fine for quoting transcribed interview chunks.

I would suggest you use these packages:

\documentclass[jou,natbib]{apa6}
\usepackage{apacite}
\usepackage{natbib}

They will provide everything you need, if you find that using \section instead of \chapter acceptable. I personally use \section as chapters, you could easily just include "Chapter n" in the name of the chapter to indicate it is a chapter.

The customised styling does not influence apa6, so feel free to implement whatever you need on that matter. Just using \quote might suffice.

If you wish to continue using the apa6 package, you could try modifying the apa6.cls file. The absolute location of this will depend on your installation, the relative path on my Windows machine being "tex\latex\apa6." Of course, make sure you back the file up before editing.

In my case, I replaced the default "jou" entry with the "book" entry in the file, from:

\@ifundefined{def@man}{%
    \@ifundefined{def@jou}{%
        \@ifundefined{def@doc}{%
        }{% doc
          \ifx\apaSix@ptsize\apaSix@noptsize
            \LoadClass[11pt,twoside]{article} % default for doc is 11pt
          \else
            \LoadClass[\apaSix@ptsize]{article}
          \fi
        }
    }{% jou
      \ifx\apaSix@ptsize\apaSix@noptsize
        \LoadClass[10pt,twoside]{article} % default for jou is 10pt
      \else
        \LoadClass[\apaSix@ptsize,twoside]{article}
      \fi
    }
}{% man
  \ifx\apaSix@ptsize\apaSix@noptsize
    \LoadClass[12pt,twoside]{article} % default for man is 12pt
  \else
    \LoadClass[\apaSix@ptsize]{article}
  \fi
}

to:

\@ifundefined{def@man}{%
    \@ifundefined{def@jou}{%
        \@ifundefined{def@doc}{%
        }{% doc
          \ifx\apaSix@ptsize\apaSix@noptsize
            \LoadClass[11pt,twoside]{article} % default for doc is 11pt
          \else
            \LoadClass[\apaSix@ptsize]{article}
          \fi
        }
    }{% jou
      \ifx\apaSix@ptsize\apaSix@noptsize
        \LoadClass[10pt,twoside]{book} % CHANGED default for jou is 10pt
      \else
        \LoadClass[\apaSix@ptsize,twoside]{book} % CHANGED
      \fi
    }
}{% man
  \ifx\apaSix@ptsize\apaSix@noptsize
    \LoadClass[12pt,twoside]{article} % default for man is 12pt
  \else
    \LoadClass[\apaSix@ptsize]{article}
  \fi
}

This at least worked in my case - allowing chapters to be rendered (as well as in the Table of Contents) for my PhD thesis.

Ed.