Combining non-isolated switch mode power supplies in parallel into a single supply
Consider what happens to your current limiter circuit under overload conditions.  If we look at one circuit alone and assume it has resistor values chosen to limit the current to 100 mA, what happens if the input is 350 volts and the load is 1 kOhm?  Since the current is limited to 0.1 A, the voltage on the load is 100 volts, so the drop across the circuit is 250 Volts and the circuit must dissipate 250 volts x 0.1 amp or 25 watts.  So one of your circuits will fail quickly whenever an overload occurs, followed by the others.

You do need the diode if driving loads with any capacitance, because if you turn the drive circuit off or lower it, the result will be a momentary reverse voltage on the base-emitters.

You do need R1 for some current limiting because otherwise Q1 and Q2 are simply diodes if they become saturated and the left-hand supply will see the entire load.

Good luck!