Attention to detail in your code and design work is important – but before you lay down one single pixel, or one single line of code, you need to make sure that everyone (you, your client, your clients client, etc) are on the same page and make sure you are managing expectations on what the desired project outcome is.
You, and your client(s), need to determine which theme framework (if any) are appropriate for the project, which plugins can be utilized to meet the goals of the project and determine which aspects of the project require custom development to account for features that existing plugins do not currently cover.
Managing expectations and properly scoping out a project is key to successful project management, both for you and for your client.