Upto you some go straight into it some stay with cat C for a bit no rules
Stay on cat C get some experience on the road ie avoiding 7.5 t weight limits low bridges using maps/electronic map ( sat nav ) getting to know the road net work using your taco dealing with driver hours good in people picking up bad habits ( probably some more that others will think of ) although you can do this driving small van or 7.5t ( c1 )
Go straight to CE still in learning mode no bad habits picked up
Don’t forget when you pass & find a job you then learn to drive same as always been same as car