How many quarts of tranny fluid should I have on hand after dropping the pan?

6 to 8, may not need them all but 6-8 usually covers it

If you are lucky and have a drain plug on your converter its always a good idea to drain that as well if your looking for a fluid change.

Of course that would require a bit more new fluid.

Seems I read 19 pints in a manual. That is with the converter. I think it was Chilton. A lot of folks don't like Chilton, but the capacities should be correct.