You didn't tell us what load (current) Q1 is driving.
Q1 needs a base current of about 10% of the collector current for maximum saturation (for a BC327, BD136, etc.).
Then the optimum value of R15 can be calculated.
Base current needed for Q6 depends on the current through R15, and can be ~20% of that (for a BC547, BC548, etc).
Then optimum value of R32 can be calculated.
Opto LED current needed depends on the minimum CTR of the opto coupler (50% for this one).
So twice the current needed through R25 as through R32.
Allow for the saturation voltages of the transistors, and Vf of the opto LED and BE diodes when you calculate the resistors.
Leo..