Maintenance Customer Conversion Rate by Employee with Time Intelligence

Firstly, just to recap a couple of things. The RevByItem table shows which items were "sold", but not which employee sold them. The ServiceLookup table contains who "sold" the item in the [Assigned To] column. The relationship between the 2 tables is best linked based on the [Invoice #] column which is obviously present on both tables and is a many to many relationship.

Basically what happens in the business is that certain employees provide an initial service and are also supposed to sell a maintenance program at that time. If the employee doing the initial service sells maintenace services than another employee, differnent than the initial service employee, comes back quarterly and provides the maintenance service. 

So what I need to show is the % of customers who purchased an initial services and then of those customers who bought the intial service which of them later bought at least 2 maintenance services. I need this info organized with time intelligenc in the rows and by employee who sold the initial service in the columns. Again keep in mind that I only care about who provided the initial service. Other employees may provide the maintenance services, but it is the employee providing the initial services job to sell the maintenance plan and I need to be able to measure how effectively it is being done so I know who is good at it and who isn't