Auto setting security settings of a subsite using workflow

I work for a consulting company who takes small projects from various clients and wants to move their document control system onto SharePoint.

I have built a workflow which creates sub-sites using a template, but my boss also wants the sub-sites to have certain security settings such that the company's staff has access to all sub-sites (reading as well as editing), but the clients with only read access to the sub-sites that are dedicated to their project.

Right now all the sub-sites inherit from the main site, which grants everyone at least Read access. Is it possible to make this adjustment using workflow?

Either within the workflow for creating sub-sites or using a new workflow, as long as it gets the job done.

I am very new to SharePoint.