I'd love to help you with setting up classes in QuickBooks Online. However, the Class tracking feature is only available in QuickBooks Online Plus. Once you're ready to have this feature, we can upgrade your current plan to QBO Plus. I'll show you how:
To add new and existing expenses to a project, we can also refer to this article: Set up and create projects in QuickBooks Online. This provides information on how we can add project income, expenses, and labor costs and run project-specific reports from a single dashboard.
To manage your sales and stocks, we can read these links: