Thank you for posting your request on History Hub.
Yes, the first step would be to request a copy of his Official Military Personnel File (OMPF) which you have done online. You may want to check the status of your request and you can do this by either email through NPRC Customer Service Center at firstname.lastname@example.org or on the following page https://www.archives.gov/veterans/military-service-records . There is helpful button at the bottom of the page that you can click to check the status of your request.
Using his OMPF you will be able to identify which locations he served at, what units he was assigned to and then begin research on those locations and units. To seek organizational records, you may post a follow-up question here on History Hub or by emailing email@example.com .
Due to the COVID-19 pandemic, the NPRC has been closed and only completing emergency requests. As of March 8, 2021, the NPRC entered into a phased expansion of our onsite workforce. While we continue to increase our on-site staffing, we are still servicing requests associated with medical treatments, burials, and homeless veterans seeking admittance to a homeless shelter. Please refrain from submitting non-emergency requests such as replacement medals, administrative corrections, or records research until we return to pre-COVID staffing. We thank you for your patience and look forward to resuming normal operations when the public health emergency has ended.
We hope that this has been helpful. Best of luck with your research.