How to remove an affect?

If the effect is still live, you can get to it in the Appearance panel (window menu -> appearance)  With your blurred item selected, (it could be an object, a group, or even an entire layer depending on where you applied it)  find the blur there in the Apperance panel, select it and click the little trash can button at the bottom of the panel to get rid of it.  You can also double-click on the effect to modify it instead, if you'd like.

If the effect is not live, you may be out of luck.  Some more details will be needed. (how did you apply the blur?)

To crop, I would think that you'd be looking for a clipping mask:

Select everything you want clipped and group it together (optional, but might help keep you organized) Draw a rectangle (actually any shape you'd like) where you want to crop your art - make sure it's in front of the art.  Select the group and the rectangle, right click and select "make clipping mask" (if you're on an old mac or something, it can also be done by selecting them both and going to the Object menu -> clipping mask -> make)

Even if you don't group them all initially, once you make a clipping mask using this method, Illustrator will collect everything together into a group, regardless of how you might've had them organized on layers, so if this is important to you, work on a copy.