Do the PI and each Co-PI submit separate notices of intent/proposals for a single collaborative project?

No. One NoI/proposal is required for each project submitted for funding consideration. Each individual PI/Co-PI associated with that project does not need to submit an individual NoI or proposal. In the NoI module you can add Co-PIs and other personnel by selecting “Edit” for the personnel page (form 2) and clicking “Add New Personnel”. These personnel will be carried over into the proposal from the NoI submission.