Since the majority of the work we do is either internal work (work for the company itself and used only by employees) or (for clients) modifying our application template with a few tweaks to functionality and a fresh skin I was thinking that the idea of doing complex, detailed functional specs and walkthroughs and use case scenarios may be a bit of overkill, but we can do it once for the default application template and mostly not have to repeat that step.
So my thought is that we start with a complete functional spec and use case scenario (based on our default application template) and we use that as the document to record which modifications we are making. Then breaking it down into blocks of tasks in a WBS and using that for our first SWAG on the estimated time to finish (ETF). The WBS would then get pulled into a project plan for better task separation and assignment and give a clearer view of ETF. While the work is ongoing, having each task as an item in Trac (or something similar) might allow a quick way to see how well we are doing on sticking to our project plan.
What have you done that has worked (or not worked) for you? Any suggestions?