Hi Daniel - I agree with the other responses that you may not have to start from scratch if you use FAI's existing competencies.
That said, you may want to carefully consider whether to include non-technical competencies in your needs assessment. Depending on what you want to do with the needs assessment, you might want to include additional competencies that are related to the job, such as various interpersonal competencies, project management skills that go into more detail than the FAI models, and even supervisory and management competencies.
Further, using online tools or software to collect the data can give you many efficiencies and provide a positive experience for the employees who are completing the needs assessment. There are tools available specifically for competency assessments that will automatically analyze and report the results for two raters (employee and supervisor) as well as give you online survey formats more geared toward competencies rather than typical survey questions. This can save you a lot of time on the back end so that you don't have to figure out how to match up employee responses with supervisor responses manually in Excel.
Finally, once the needs assessment has been planned and you are ready to roll it out, the communication of the assessment is critical. Employees often want to know why the needs assessment is being done, how it might impact their annual performance review, who will see the results, and how the results will be used.