[2.6] Chaos Caster - looking for feedback + answers

Hello, I'm thinking of starting a Essence Drain/Contagion/Wither character and I would like some feedback on my planned build. Any improvement suggestions would be appreciated.

End-game build (killing all bandits)
www.poeurl.com/besL

For lower point leveling progression I guess I would probably go towards Zealot's Oath first, taking some ES along the way. After Zealot's Oath I would build up the branches in the witch/shadow area. I would leave going towards middle Scion area for late game.

I've seen that a lot of people are using Wither totem and I'm curious about why this is so. The lower cast speed of totems I'd imagine would lead to low wither stacks. Instead I'm thinking of doing Wither - Cast while channeling - Essence drain and I'll maybe use contagion totem. Would this be a bad idea?

Thanks for looking though and I'd greatly appreciate any feedback from experienced players.