No sand blasting required to clean rust pits.
You've done a perfect job that's ready for epoxy primer that will not allow further rusting. That's the job epoxy is so so very good at!
If you read the tech data sheet on the epoxy you are going to use, they will refer to SSPC2 or SSPC3 clean prior to applying it.
Here is a link to what those those mean.
http://www.blastal.com/images/SSPC_Chart.pdf