50V 10A is pretty ambitious.
A lineair supply would need to be able to dissipate 500W in worse case condition.
That is like a big CPU cooler for each of your 4 power transistors.
Do you have a good reason for this power requirement?
In my experience, I can do most projects with 30V 500mA power supply, and when more power is needed it often does not have to be well regulated.
You are also likely to want to have multiple power supplies. So even if you first design / build a small one, then you will still use it after you built the big monster.
I also agree with kallek. Use a uC and dac to make a setpoint, and use analog circuitry to regulate the output voltage.