a few ideas…
Helm - not bad, but ideally you want 6% CHC and 15% Multishot
Shoulders - roll armor for CDR
You have Fire Resistance on these - not Fire Damage - so roll the life per hit to Fire Damage % (20%)
Quiver - roll the VIT to 15% Multishot damage
Bow - your Yang’s rolled with nearly the lowest bonus damage (155%) so finding another one is a high priority - ideally 190% or higher.
Swap (as Varadia said as well) from Fan of Knives to Preparation-Invigoration for the extra 20 Discipline which will be a massive boost to your damage.
Swap Ambush to Steady Aim - SA will provide more consistent damage to mobs versus Ambush which drops off after only taking 25% of monster health.
Swap Stricken for Molten Wildebeast’s Gizzard - Stricken is most often employed in higher GR (100+) and the shield provided by the Gizzard gem will help you 1) keep up the squirt’s buff for your outgoing damage and 2) help you from taking that big slam from the squirt’s incoming damage debuff.
I would honestly roll one of the rings to 50% CHD, will actually be better for you to have 1 6% CHC and 1 50% CHD since your CHD is currently really low.
Any DPS stats you have rolled onto gear - try to get the max (like on your gloves try to get to 48-50% crit damage and to 15% MS damage on boots/helm)…
Paragon - since you are still under 800 and we can’t see what you’ve allocated, I’d recommend the following:
Offense:
Max out CHD, CHD and CDR and then remaining points into Attack Speed
Defense:
Max out AR, Armor, Life, then rest into Life per Second
Utility:
Max out RCR (big defensive boost with the Cap Crimson set), RCR, Life per Hit, rest into Gold Find
Core:
Max out Hatred and Movespeed, rest into Dexterity
Cube:
Replace Obsidian ring with one of these:
Visage of Gunes to get 50% damage reduction while Vengeance is active (should be always)
Magefist - for a 20% fire damage buff
Convention of Elements - up to a 2.25x damage boost (on fire cycle) - but this will only work this Season due to the Seasonal Theme for the Cube.
Elusive Ring - another damage reduction option (60% after vaulting) that only works this season…
Understand that Ancient/Primal is not always better - an ancient UE helm with Dex/Life%/MS is likely going to be WORSE than a regular helm with Dex/6%CHC/15%MS…
Finally, have fun with UE. It’s a dependable do all for everything except pushing high GR. You mentioned the Nats RF, but that requires really high paragon to be much good. For most, the Shadow’s Mantle (S6) build would be up next for pushing…
Happy pew pew’ing!