Voltage and Current sensing
High side current shunt IC's exist. Otherwise DIY current shunts drop only 50mV at full current to limit Pd in the shunt and require high gain. This could be done on either ground or supply side as the drop is negligible. 

The biggest problem is using a series pass regulator for a 450W supply will dump half of this in the series pass at half Vmax out at max current.

Thus a Buck regulator is the only efficient solution, which is well documented everywhere.