If you plan on using sorceries, the Izalith Staff is the strongest staff for this build. The following equipment benefits most from dark magic builds: Izalith Staff If you plan on casting sorceries, having a Scholar's Candlestick on hand will provide a 25% boost to sorcery damage. It's a good idea to have a raw infused weapon that you can buff for boss fights, but general damage can come from your chaos or dark infused weapons. I generally like to mix damage types and since this build focuses on dark magic, I'd use a chaos-infused weapon in order to deal with dark-resistant enemies. Since your stats are heavy into FAI and INT, dark and chaos infused weapons are good. Winged Spear is also D/C/A/A (12/15, 6). A Crystal-infused Saint Bident scales E/E/C/C and is reasonably strong, especially for the 12 STR and 12 DEX requirement.
Use Dark Sword (16/15) or Astora Greatsword (16/18). 16/18 is a nice stopping point for most weapons, but you can save a few points by sticking to a Dark Sword (or even an Estoc). Find a weapon (or a few weapons) that you like and adjust your stats according.
Your STR/DEX stats are somewhat flexible. Note: Equipping a Prisoner's Chain in one of your ring slots allows to reduce VIG, END, and VIT by 5 points each, freeing up a total of 15 points that you can spend elsewhere.
