Multiple voltages power suply, high current
This is a no-go. The power which you have to dissipate in the diodes will be enormous.

diodes between 12V and 5V dissipate 7V @5A = 35W
diodes between 24V and 12V dissipate 12V @7.5A = 90W
diodes between 48V and 24V dissipate 24V @17.5A = 420W
Total amount of dissipated power (in diodes) = 545W


The diodes able to withstand such power need to be extremely big, the absorbed power will all be transfered into heat so you would need giant cooling fans or a very big airflow.

This kinds of power really need to be converted by a switch mode conversion which will give you an efficiency in the order of 85%+.
Instead of dissipating 545W in the electronics you now only have to dissipate 15% of the output power, so 295Wx0.15=44.25W
Still a lot but way more feasible.

So you better go looking for three switched mode PSU for 48V>24V, 48V>12V and 48V>5V