I have been talking to some people who are much smarter than me when it comes to analog circuit design and we have come to the conclusion that it might be a safer route to go with a ready made LDO, ideally something like an LT3083. The LT3083 is a 3A regulator that allows the output to be adjusted right down to 0V. Chosing a ready made LDO also makes it much easier to get the circuit to be stable over the full output current range and I don't have to spend ages trying to stabilize the MOSFET circuit.

I am still not sure as how to choose the inductor and output capacitor values for the LM2576 in my situation. There is an example in the datasheet of a 1.2V-55V 3A adjustable output voltage supply but the values that I get using the recommended component selection procedure in the datasheet just don't seem to match up with the values they indicate in their example circuit.

Unfortunately as a student/hobbyist I am a bit limited in component selection here in Germany. There is a very promising switchmode regulator by TI the TPS4331 which seems to be a more modern version that operates at a higher switching frequency which helps reduce the physical indcutor size. If I was able to use that I could save board space and probably have a slightly more efficient tracking pre regulator.

Asking over on the EEVblog forum about this issue didn't get me any useful replies so I might have to change the pre-regulator.