Coulrophobia, Thana, Sloppy, Dying Light
As far as I'm aware, yes, they do stack.
Yes, they do indeed stack.
Usually if a perk doesn't stack with other perks, than it would usually indicate this through the description itself. Something like "This perk does not stack with others" or "This perk isn't stackable" would be written under the perk itself to let you know if it stacks or not.
That doesn't mean EVERYTHING stacks without this description, it just means most things should stack with each other if this description isn't present.
Yes they all stack although idk why you would even want to run this build together. Sure heals in Terror radius would be pretty slow but best possible outcome is a 31% slow-down with 5 stacks of DL and 4 from thana. At that point you have pretty much already won the game. That aside the best you could get is a 46 meter terror radius with doctor with both calm addons which isn't even that big , so most likely coulrophobia wouldn't really be that useful.
Combo perks on killer leads to win. You re such a boring .
If you use it on The Plague or The Legion than you already hit 4 stacks of Thanatophobia within the first few minutes of the match. The rest relies on your ability to down other Survivors without losing Generators in the process.
This mostly works with The Plague since they stay injured the whole match to avoid "Super Vomit", for Legion it's better to run perks that increase healing speed, since that wastes MORE time for the Survivors that heal to avoid Thanatophobias penalty.
Besides that though, this build is only really good on Legion and Plague and that's about it.