While there is nothing blatantly wrong with the schematic in post #1, it does have room for improvement.
1. There is no reference voltage and feedback, so this is a crude "regulator" whose output will increase as it warms up. Depending on the transistors, that increase could exceed 0.25 V.
2. The design lends itself to thermal runaway. As a BJT (bipolar junction transistor) heats up, its base-emitter junction forward voltage decreases. Even with individual base resistors, the transistors with the lowest Vbe when cold will conduct the most current, heat up first, and conduct more current as they starve the cooler transistors with higher Vbe's. The solution is a small power resistor in series with each emitter. The larger the resistor value, the more power is wasted. BUT, the less the individual Vbe's matter and the better the current sharing among the output devices.
3. There is going to be amps of base current trying to go through the pot. Power darlington's make the thermal management issues worse, but reduce the base current by 50:1.
4. Power MOSFETs do not have the thermal runaway problem, and naturally current share better than BJTs. But the transconductance is much more temperature sensitive, and in a follower arrangement there will be a much larger voltage between the gate and source than between a base and emitter.
5. Rethink your fan size. With a 4 V input, 3 V output, and 150 A, the transistor array will develop 150 W in component heat. If the parts are all in a row on a heatsink, the ones away from the fan are going to be "cooled" with very hot air, so the air flow has to be increased to cover that. There are many fan calculators on the web. Here is the equation for the best-case, perfect condition where 100% of the air touches 100% of the hot component surfaces. You derate from there.
https://www.nmbtc.com/fans/engineering/airflow-formula/
ak