[...] i have to mill 4 legendaries to make the one i want?
correct
is there anything i am missing?
maybe.... lets get through the other questions first...
is there another easier way? through the story book maybe?
Yes. For other leaders you can indeed get them from the Reward Book (total cost ~140 reward points for all of them). For other cards your main method of getting them will be from kegs, and from random drops from daily awards.
also the dust that makes premium cards why there is not an option to craft actual cards with this?
Because it's only meant for visual/status goodies, not things that affect gameplay
why would a new player want to craft premioum cards?
They wouldn't. The only difference between regular and premium cards is that the premium ones are animated.... that's it. New players should be getting most of their new cards from kegs, and a few from crafting with scraps from milled duplicates.
from my point of view first priority of a new player is to get as many cards as possible, then make the good-looking cards.
this is correct, but you shouldn't worry about making premiums until you have nearly (if not the entire) normal set. you WILL get some, but they are not important until you get most of those normal cards.
for fastest effective completion of the set, you should mill any cards you have more than the usable limit of (this is automatic if you only have normal, or only have premiums of that card when using the "mill spares" button. you have to do it by hand if you have mixed copies of a card). you should spend all scraps on the most expensive normal cards first (Gold Legendaries [gold pip, not pink], and if you don't have thronebreaker, normal thronebreaker cards [4x normal cost]). and obviously earn as many kegs as possible. It's worth it to break the above rules to craft a card you need for a deck, since winning ranked matches can provide a lot of kegs at season end.