Please visit the Contractors State License Board for information regarding hiring a contractor and to verify if a contractor is licensed and insured: http://cslb.ca.gov.
When all wallboard has been installed and nailed or screwed in.
Plan check is not required for existing systems that are added added or altered with branch lines serving less than 20 fixture units and sized per table 610.4.
Depending on the project, there could be one or as many as needed to complete the project.