Hi @Harry
In Acumatica, projects are company-specific, so the best practice for intercompany work under one job is to create a mirror project in each company and use intercompany AR/AP transactions to move costs between companies. Each company records its own expenses in its own project, and intercompany billing is used to transfer charges. Billing rules can be configured on the Billing Rules (PM207000) form to control time and material or progress billing .
To restrict visibility, keep each legal entity as a separate company and control access through roles and user company assignments. Users should only be granted access to their respective company (and branches if applicable) to ensure Company A data is not visible in Company B and vice versa.
Hope this helps.