The answer to the first is simple. You are using the wrong thing.
Instead of creating a 3 edge you need to create a Planer surface.
3 edge is for a a part with x,y,z depth while the planer surface is a flat plane of any shaped contour.
I will look at your file for the other.
Update. It appears the trouble comes from the razor edge you are trying to create using extrudes/skins/surfaces. This is not going to work.
Try placing a flat on the knife end (make it thicker not shorter if you wish to keep the length) and then later you can use booleans to make the knife edge if you like.