Hi @chanokns,
What is your data source here?
If you are using a SharePoint list, there should be a Modified field which could show the Update time.
For other data source, you may need to add a Modified time manually, and update the time within PowerApps accordingly.
For question 2, we could take use of the sum() function to calculate the totals:
Sum( Table, NumericalFormula )
Function reference:
Average, Max, Min, StdevP, Sum, and VarP functions in PowerApps
Question 3: could you please explain a bit for report User Lists? If you would like to record User usage, then we could create a table recording user sign-in information (thread reference: Patch Timestamp).
Or if you just want to check the App usage, check the article below:
App usage report- Monitor how many users are using your App within your organization
Question 4, do you mean the Home screen of web.powerapps.com?
The structure under web.powerapps.com is predefined, if you would like to add customizations to this page, then please consider submit an idea on this, through the forum below:
https://powerusers.microsoft.com/t5/PowerApps-Ideas/idb-p/PowerAppsIdeas
Regards,
Michael