Enemy slow and cast on bow attack (poison)

I am planning for next league a meme build. Yes next league i like to be prepared :).
The idea is to use on hit + slows + poison. I mostly have questions relating to slows on enemies.

1 Does movement speed slow also affect things such as casting speed? Just movement speed or also casts that include movement?
2 how do sources of slow stack?
Lets say Maim + chill is it added together and subtracted or are each subtractated after eachother?

As for the build i am not that far with it, but if you want to have a laugh or have any suggestions let me know. Core elements:
Life/mana on hit
Hit a lot with poison
Slow/debuff enemies a lot.
I am doubting between pathfinder and occultist, but i think occultist is better.

https://pastebin.com/cUM5JK2S

Thanks for reading