Welcome to the game and to the forum. 
This is what we call an endgame build so optimised to be the best it can be. This sort of guide doesn’t include things like levelling, devotion pathing, etc. For that you should look at the Beginner’s Compendium to see if you can find a similar build to use while levelling and then respec at the Spirit Guide once you have the necessary level/gear to do so.
You will start finding Legendary items once monsters are L50 and above, but yes, you will need to reach higher difficulties and probably have to farm for some of the gear.