Firstly, and most importantly, the decision making process for these key points must allow you to ascribe a value to the elements needed to achieve the benchmarks you have set yourself.
Secondly, you should set out how you will approach the assessment. This would include both the tools you might use (such as an AEDET or ASPECT workshop) and the information you will need to inform the decision: i.e. the shortlist of sites for selection are likely to require some level of design feasibility study to provide reliable information on whether the 'Non-negotiables' can be delivered on the site and the implications of doing so.
For example, a site that is ideal in terms of transport connections and immediate availability may be very close to a busy road and therefore building on that site will require significant investment in the building envelope (wall and window construction) to attenuate sound, and a more sophisticated building layout and section is likely to be needed to allow the use of natural ventilation to keep the development within the sustainability criteria. This knowledge may either prompt the choice of a different site, where all of these factors are more easily achieved, or if this site is still the preferred option will allow the proper planning and budgeting of a project on this site.
The information required to make good and informed decisions at these key points needs to be allowed for in the programme and budget of the project and therefore the process of self assessment must be understood early in the project to allow the proper planning of this.