Im looking to craft a damage over time multiplier, but what i should be looking for extra before crafting the chaos damage on the crafting bench?

+1 level of all chaos gems and/or +1 level of all spell
spell damage

I think I'd go bow tbh, with +1 level of socketed gem / dmg over time / multimode : +2 level of supported gem + chaos dmg over time, with an empower in the link
would allow you to get a 6link essence drain aswell in the armor, for maximised single target dps !

Being bow doesnt mean he woul have to change a couple skill/tree skills?