When you say they need to filter on those records, is that because they need to report on them? If so, that doesn't necessarily require they be part of the Project record itself. It may be sensible to have one or more related record that captures the data, then when building the Platform Analytics Dashboards to show the output, you can use Related List conditions to filter data by those records.
Try not to lose sight of the core functionality of the Project record: It's about dates and times, managing costs, and making sure nothing gets missed.
In terms of your fulfilment process, Playbooks are very intuitive. Head over to the Playbook Designer and look at the default Playbook for Projects (or Demands if you're on an up-to-date version). The majority of steps are just instructions to the Project manager, and you can add questionnaires to the Playbook to capture data points that only influence what task needs to be done next, and doesn't need to be reported on. Once that's done, set the playbook's trigger to run on creation of the type of project you're working on, and you'll see it in the Project Workspace.
