Queries creating a workflow on Sharepoint Online via Flow

Hello All,

Let me first state that my knowledge and experience of both Flow and SharePoint only goes back to about 2 days worth of testing, so please bear with me for the gaps in my knowledge and I apologise in advanced if I am asking obvious questions.

I have been asked to create a process which utilizes document management, version control and can then be approved after a period of time has lapsed. This process would be run hundreds of times throughout the year and will effect various different users within the business.

With my limited knowledge of SharePoint I know that this ticks a lot of boxes so have been testing to try and make a business case for us to use SharePoint Online, which we have through our Office365 account but do not use at all at this moment.

So the process that I want to try and create is this:

1) The Finance team create a new folder on SharePoint and place within that a budget sheet .

2) An e-mail will go to another team member telling them that the budget sheet is ready to be edited. This person could be one of several so I need the ability to be able to choose who to send an automated email to.

3) A timer is placed on the workflow with regular reminders. I have manged to partly achieve this by using the Delay Until step and adding so many days till a reminder e-mail is set.

4) I would like to be able to then start an Approval process after the user has finished amending the budget. The only way I have been able to think of doing this if they move the sheet to a new folder which then kicks off an approval workflow. Is there a more convenient way?

5) The approval goes to 4 people, again some of these approvers can vary so is there a way to distinguish who it should go to?

6) Once approved I would like the document to actually be marked as approved somehow. We don't have Docusign or any electronic signature software and I know that the business will not invest in one at this time so I am trying to figure out if the document in Share Point can be set to Approved or comments are automatically updated etc. I have tried using the Set Content Approval Step but get a 409 status error message (below}):

"{
  "status": 409,
  "message": "{\"Etag\":\"\\\"{21397492-DBFE-4855-9793-996DA580CD14},3\\\"\",\"Message\":\"The ETag of this item does not match the one used for setting content approval status. The contents of the item may have changed before the action was completed.\",\"Succeeded\":false,\"ApprovalErrorCode\":\"etagMismatch\",\"ApprovalLink\":\"https://firstinvestments.sharepoint.com/sites/ServiceCharge/Shared%20Documents/Test/Service%20Charge%20Test.xlsx?etag=%22%7b21397492-DBFE-4855-9793-996DA580CD14%7d%2c3%22\"}\r\nclientRequestId: ae8c96b9-a59b-4a7e-872b-47deab7b161d\r\nserviceRequestId: 9476659e-50bb-5000-81b7-dda1deaa359e",
  "source": "https://firstinvestments.sharepoint.com/sites/ServiceCharge/_api/SP.APIHubConnector.SetApprovalStatus",
  "errors": [
    "-1",
    "Microsoft.SharePoint.SPConnectorException"
  ]
}"

Again, I apologise in advanced if there are any obvious questions within that, but if anyone can assist and point me in the right direction I would greatly appreciate it.

Regards

Richard