Changing dates from 4 weekly to monthly

Im trying to build my sheet to help manage portfolio of properties,

I need to capture all the data on one sheet, im having problem with recording monthly / 4weekly payments, i somehow need the dates to change if i flag that it is monthly / 4 weekly payments.

The only issue is that as the rooms are rented out separately, some rooms maybe monthly, some maybe 4 weekly based on the given start period, and pull through the rent due into column C-G. The room can change within the year from being monthly to calendar.

Please see column AS for the tenancy info.