You are correct that any MQD from flights paid for and not yet flown will not appear in your mileage activity until after the flight.

You are also correct that you will receive MQD for flights paid for with miles, at a rate of 1 MQD for every 100 miles spent.

Note that you do not receive MQD for taxes and fees.

I am not sure what you are referring to re the "pending" information. That only ever shows a total estimate of MQDs- it does not break out on a flight by flight basis. But you might find previous threads helpful, including

https://www.flyertalk.com/forum/delta-air-lines-skymiles/2146979-pending-mqd-activity-seems-off.html