error amplifier compensation

Hello, I am working on PSFB DC-DC converter and I prefer analog control so I need to pick a op-amp for type 2 compansation . I also add buffer op-amps in current or voltage feedback paths for stability. Which specifications should I concern for fast response ? and Can you give an example...

I bought a power supply adopter (old, used, made for some device) of 24v 4.5A (from 230vac mains). It is a fixed output psu. My intention is to make it a variable psu of 30v to <=5v (as low as possible, and continuously variable). Schematic (simplified) of its error-amp circuitry is attached...