I just have a folder for rental statements. I have never had much problem with receiving statements to need to monitor them, but occasionally notice I have missed saving one to the folder and then have to go back through my emails or follow up with agent.
Statements are a minor part of it because you get a year end summary for tax anyway.
I have many folders and sub folders for my property investing, a bit anal in records, not just for tax but more for my own reference.
I have an Excel spreadsheet with different pages such as below. Other than rental income/PM fees which is updated at end of year, all other page totals automatically update my front page tally so I know what the property owes me to the cent.