How much fender and leaf clearance is needed?

So I just got my new tires mounted and I installed them on the car. The fronts fit just fine but the rears are tight (Which I knew would be the case). I have about 1/2-3/4 inches clearance to from the tires to the leafs. The fenders are real close, so I'm going to have to trim that.

But do I have enough clearance between the leafs? I can put my fingers between so its not thaat close.

And when I cut the inner fender lip what can I put on to make sure it doesn't rust?