Crossbow Priorities
- Attack Speed
- Projectile Skill Levels
- Elemental Damage to Attacks
- Flat Lightning
- Dexterity/Strength/Physical Damage
DON'T GET ONE WITH PHYSICAL DAMAGE RUNES. You want Attack Speed instead
Morior Invictus
I personally think the best one is %Attributes + %Mana with 5 sockets. Mana spend is very high, so having a good pool so that it never dips feels very good. Super endgame budget is probably %Attributes + %All Ele Res
IMPORTANT!!!! - The chest rolls several different mods, make SURE you get %Attribs at a minimum. %Mana is secondary but extremely nice.
Rings
Fix any resistance issues you have, then prioritize Dex/Int/All Attribs, then Mana/Life. Flat Lightning Damage to Attacks can roll quite high here, if you can get it do it.
Boots / Helm
Fix any resistance issues you have, get as much movement speed as possible. Ideally you'd have Energy Shield bases to take advantage of 
Grim Feast's ES doubling and sustain. Flat Intelligence is also an important stat to look for.
High budget can go for 
Black Sun Crest but it will apply more pressure to your resistances, so you'll probably want the %All Elemental Resistances flavor of 
Morior Invictus
Amulet
Best in slot is an 
Astramentis but it's not necessary AT ALL. I used a 
Lapis Amulet with %Increased Maximum Mana and %All Attributes/Int/Dex which can be found on trade for 1/20th the price of an Astramentis and function just as well. For context, Astramentis is about a 25% dps increase.
Annoint options: 
Branching Bolts for clear, 
Step Like Mist for movement speed, 
Insightfulness for damage / int
Mercenary
Gemling Legionnaire
Hand of Wisdom and Action 
