How do I deal with items that I need to repeat monthly?
You shouldn't try to do too many things with one data store.

If you have a table for transactions, then just keep transactions in that table.  Don't mix in scheduled future transactions with current transactions.  Actual (historical) transactions will have different attributes (columns) than future, scheduled transactions.

Keep the recurring/scheduled transactions (like rent) in a separate table.  When the rent is paid, create a new record in the (actual) transaction table.

The scheduled transaction table could have a totally different structure.  Instead of keeping a record for each expected transaction, you could keep one record with a date range and recurrence fields.  This would save having to update multiple records when the rent price changes, for example.  Consider something like this for your scheduled/recurring transaction table:

Scheduled_Transaction:=


CustomerID
StartDate
EndDate
Recurrence (monthly, weekly, every two weeks, - whatever you need)
Amount