A PVE weapon would definitely boost your damage on mobs. At +12, a Bloody Retributer will favor you more than a Dark Caster + sigil. A +16 Bloody weapon would definitely be a good upgrade you can also buy 2h Bloody Runes to check the difference on the PVE damage.
You can try minor upgrades, for example getting a 30 day Anakim or Freya Agathion (all STATS +1) to add to you Taurus bracelet, and use the Tersi charm as secondary after that.
Magical and Death are great options. When you get the level, try to add Master's Rage as well.
+11 Aden cloak is really good. If you can find the stones, a +% PVE augment or a +7% m. crit damage augment are great and you can use the adena of +15 Aden cloak for other upgrades in the char.
Since you do CoC, this probably is not an option, but a Bloody Set (even at +8, as a secondary set maybe) gives you +10% more M.Attack than a Dark Set. So it's always an extra boost for pew pew
The skills, you're already on the right path, basically everything to Power and some debuffs to Chance. You'll notice a lot of difference in +10/+11 skills. Then at +16. Then at +20. But it's something costly and it takes time, so they can stay as they are for the moment.
In terms of attack, I would go first for an Insanity talisman first and then the CoC belt. Monkey Belt gives you more +2% damage, but less -1% damage received than Tiat's Belt (5% instead of 6% on Tiat's).
In terms of cost / effect, level 4 brooch jewels are great.