Customers not onboarded report

Within Prospect CRM a customer is considered as onboarded once they have placed four or more orders.It would be useful to have a report that shows customers that have not been fully onboarded. The report should show:

All customers that have placed 3 orders but not a 4th order, or placed 2 order but not a 3rd.The report should also be filtered to only include customers where the 1st order date is within a specific period such as last 4 months, depending on how frequently customers order. Instead of the first order date, the last order date could be used.

The benefit. of this report is that customers can see which of their customers are not fully onboarded and take steps such as calling, emailing, sending samples etc to engage with the customer and get them to 4 orders.