I do not think that's necessary, as long as there is a revision history and the project manager takes her job seriously. And if she does not, we're screwed whatever the process.
I would prefer for the project manager to be the person handling the spreadsheet, and the person taking care of the payment handling FreeAgent. This is for easier accountability: if the spreadsheet is messed up, it's my mess. If FreeAgent is not up to date, it's your mess.
This makes sense also because the latter is a director (in my proposal at least), guarding the official accounting that forms the knowledge base for tax returns, grant proposals, due diligence tests etc. The project manager (who could be or not be a director) stays responsible for the spreadsheet, which is an internal planning document and a forecasting tool (in the part concerning the cash flow prediction), but has no legal value or implications.
Overkill, IMHO. FreeAgent has a handy search box. It's simple to find anything in it. Stay minimal, man!
This is great, but I guess we could implement a MVP without it. Just as long as the spreadsheet template is easy and well thought through. That is where I would invest brainpower.
Yes. This is more resilient (many spreadsheets) and coherent with the project sovereignty principle.
You are right. I will add it to my proposal. I think what needs to happen is that the project manager is responsible for the document justifying the payment being uploaded onto FreeAgent. In practice, the PM might have collaborators send her a bill, or create accounts for them so that collaborators can upload their own bills. Once that's done, she starts the process, requesting the payment.