You obviously know quite a bit about servicing vehicles so I don't want to step on your toes too much SS.
I'm not a big fan of flushing transmissions, especially on older vehicles unless the owner is prepared to replace all the seals. Drain, check fluid color and inspect the magnets in the pan will give you a good idea of what is going on.
You can always do a poor mans flush, which will be cheaper although more work for you. You're paying for 2x the volume of your tranny in fluid plus labor. Drain and refill, drive for 500 miles, and drain and refill again. The most important thing is knowing the exact type of tranny fluid your car requires. Friction modifiers vary between brands and manufacturers.
My only recommendation would be to get a couple of mason jars and fill the first jar with drain #1 and the second with drain #2. Compare them after the second has settled overnight on the workbench and look for sediment in the bottom of the jars. It's probably overkill, but it helps you understand the vehicle.