Order MD ammount tracking (issue summing)

Business requirements:

We got a lot of customer, who are making orders from us. We are providing a human power to them and they are invoiced in MDs.

The problem is, that each order should be trackable in the point of view already spent hours / MDs with the particular order and with particular customer. 

On each order will work more roles, will be in more projects and will have to be independent on epics.

Solution proposal:

Technical details of the solution: