Been a long time since i played skyrim. Was thinking of playing it again thanks to a new ENB mod
but i have a few questions:

Depth of Field- Does it affect performance and frame rate as heavily as SSAO? Is there a big difference between no dof and dof?
Blurriness- What does it mean? Radical Blur or AA?
SSAO- Is there an alternative to SSAO? I dont want to lose 25 frames for something not significant.

You can turn off SSAO in the ini if you don't want it. Personally I consider the fpsdrop worth it though (but I get a decent fps with it on so np). You could also use the performance SSAO setting which is a lot faster.
As for DoF, it does affect performance and it varies a lot from person to person if they actually like it. I have never been a fan of the bokeh-style DoF, I find it awful. The difference is big both in performance and look.
Not sure about blur.

Blur is what the mod does nativly..