I’d love to be corrected on this if wrong, but I don’t think you can currently do what you are requesting, since OF does not allow you to set an end date for repeating tasks (an odd omission).
Right, I understood that. My point is that I think the two features (setting an end date and setting a number of reps) seem like they’d be interrelated (think of the iCal app), so that not doing one implies not being able to do the other.