よりシンプルに...

f(x) := (-1)*Σ[k=1..n] C{n,k}(-x)^k / k
f’(x) = Σ[k=1..n] C{n,k}(-x)^{k-1}
　= (1 - (1-x)^n)/x = (1-(1-x)^n)/(1-(1-x)) = Σ[k=0..n-1] (1-x)^k

Σ[k=1,n] C{n,k}(-1)^{k+1}/k
　= f(1) - f(0) = ∫[x=0,1]dx f’(x) = Σ[k=1..n] 1/k

問2をこの方向でやるのは却って面倒かもしれない.