Well, you got that diagram wrong!
You show E1 to E4 connected to ground instead of the phototransistor emitters.
The optimal LED current will be in the 10 to 20 mA range - as your graph shows. Let's say 20 mA and a 100 Ohm resistor. Worst case CTR is 0.5, so you may expect 10 mA from the phototransistor, at 24V that would correspond to 2k4 and the resistor would dissipate a quarter watt. I think 4k7 would be a more conservative choice (if you needed them - see below).
Do we know yet what the input characteristic of your 24 V device is? Since the datasheet refers only to switches pulling up to 24 V, you do not need pull-down resistors in any case.