The extra skin is a tricky one, but you already have done it. It really depends on how invisible it is for you. If its super invisible i would leave a little tiny bit at the front hairline, but most cut it right to the hairline. when u cut lace or skin right to the hairline, it makes attaching the front a little more difficult if you expose your hairline. What i mean is when you comb your front hairs back , it pulls right on the edge of the skin/lace and wants to lift it. having the little extra in front prevents this.

With skin pieces I usually use a little bit of white glue at the very front center and the rest including my temple flaps i use got2b