Does your institution not specify where to put an acknowledgement section for your thesis? Usually they have pretty draconian rules about that sort of thing. Personally, I think that 2 seems like a terrible choice for a thesis. For papers, you typically have acknowledgement, bibliography, appendices, in that order. For a thesis, the acknowledgements should be in the front matter.
For example, one thesis guideline I'm looking at right now shows dedication, epigraph, table of contents, lists of {abbreviations, figures, schemes, tables, etc.}, preface, acknowledgements, vita, abstract, introduction, etc. So that's similar to 3 except that the abstract comes a long way after table of contents in the front matter.
I guess I don't really have an opinion about 1.
As noted in the comments your code does not produce a new line so there must be a blank line in the document.
The standard latex mechanism for producing displayed environments is to use list
or \trivlist
If you do this then it handles ignoring blank lines at the start and merging any space before or after the environment.

\documentclass{article}
%definition of quote with addition of [\textbf{Abstract --- ]
\renewenvironment{abstract}
{\list{}{\rightmargin\leftmargin}%
\item[\textbf{Abstract ---}]\relax}
{\endlist}
\begin{document}
\begin{abstract}Red yellow blue\end{abstract}
\begin{abstract}
Red yellow blue
\end{abstract}
\end{document}
Best Answer
I went with:
This way both look similar and good.