Am I calculating a pull-down resistor correctly?
5mA is quite a bit of current to &quot;waste&quot; for a pull-down. You should calculate how quickly you need to pull it down, estimate the capacitance and calculate that as one limit. Then look at the leakage (as you have) worst-case, and make sure there is adequate noise margin below Vil under worst-case conditions.
Leakage is 1uA maximum over the full temperature range (very important that it is over the full range) and Vil is maximum 0.8V. If we allow 400mV of noise margin, then the resistor should be no higher than 0.4V/1uA = 400K.
If we assume a 1us glitch is acceptable and we assume input, output and stray capacitance adds up to, say, 10pF then the resistor should be lower than about 100K.
Finally, we'd probably like a bit lower impedance than that for reasons of noise immunity and possible PCB contamination, so maybe we pick 10K or 20K. But if there's a ground plane under it and the PCB is in benign conditions 50 or 100K is also valid.
If you don't care about efficiency, elegance etc. your lower limit on the resistance is set by how much the push-pull output is guaranteed to be able to drive (over temperature) and still yield acceptable noise margin (relative to Vih of the MAX chip).