Need help with build for GR 20 and Torment IV Bosses

I chose Wizard as my first class and have about 20 hours in total on Diablo 3. I beat the campaign, started adventure and just wanted to finish the season. I got to the part in the season where it wanted me to use Kanai's Cube to upgrade a rare and buy a weapon from Kadala using blood shards.

I decided to buy a source from Kadala and use my primary wand on Kanai's cube. I got an Ancient Legendary Etched Sigil from Kadala and a Legendary Serpent's Sparker from Kanai. That's my best gear.

I mean as of now my gear is pretty bad, trying to do Torment IV Belial is literally impossible. His primary attack will bring me down to 40% health, and his other attacks will instantly kill me. I'm using these skills, and I think they're okay. My pants and source both have 15% more disintegrate damage, so my best source of damage is to freeze them and disintegrate them.

I mean i'm still using Cain's set, so for my build I need everything but a weapon.

Where do I even start? Do I do nephalem rifts until I get enough shards to buy gear good enough to do greater rifts? Or do I go right into greater rifts? Should I even bother with rifts or just convert rare's into legendaries? All help is appreciated. Also I have on friends with Diablo 3, so I have to solo everything, so getting a partner to do Greater Rifts isn't possible.