I start off practising without distortion this helps you learn to hit the notes cleanly and clearly without "hiding" behind the distortion. Then I used crank up the dis just cos it sounds good. But after I've a lil work out.
As for the hitting the strings hard. Yeah Zakk does hit them damn hard. I think this is also just to get a nice clean sound of a note. I don't pick notes too hard, but hard enough for the note to be crisp. (I do like my descriptive words begining with a c, lol)