Customer Email Task List Creation

Looking to create a small webpage to manipulate data from a spreadsheet and send task list to email of salesperson. I would like a back-end page that is password protected and contains the database listing and tasks list based on the last sale date of the customer from the database. It has to be a calculated date to stagger the tasks out over the month. After the sale date the customer should receive a letter at 45 Day intervals and a phone call at 90 day intervals. This would have to be determined from the data that is imported from the CSV file that I will provide. Would have to be able to insert and remove salesperson emails to match records of active salespeople and be able to reassign should a sales person leave.