For a newbie you have a reasonable choice of legendary items, although an elixer mythstone would be better for the sets and the aftermath robe isnt actually too good, you have done a good job…
For improvements, i would say to use some diamonds on the head and amulet for the +5 all arch mage because it will raise your base damage a decent amount
use some calcite to make it all one element, from your build i surgest poison (although i dislike the element, it would go well with some sets that come with it) but until you can get the setds with that, i surgest ice to freeze targets preventing them from attacking you…
Your orbs weapon damage is useless to the meteor damage, unless you can kill with shatter its not needed, you should change the element and use sapphire to re-role that to elemental damage (both +5000 and +25%) for the head, swap that +20% mana to +5000 mana (greater benefit from cosmic power)
Some more i could tell you to do but sounds like your a little fresh for those, but change the rings +17.9% elemental damage to +5000 elemental damage.
Cuzeg has an aftermath guide, ill find it shortly, you should read it if you havent already and it should give you some advice on what to look for in your gear
Also yor talents are great, keep them for your current build…