Enable Association Between Project and Invoices/Quotes

We’re a green construction company and want to use projects to track our installation projects and service work using projects. However, we need to associate invoices and quotes to projects. The reason for this is the customer pays in installments/milestones, which is part of the project management and we don’t want it just on the sales deal. We also want to accurately job cost all of our projects. This would be a HUGE help for companies like ours, but really for any company that does any sort of implementation and milestone payments are part of project managements. Also if you could make the Projects API public that would be great as well!
Note: my idea category/product url don’t make much sense because this is kind of an overall hubspot feature request.