I don't agree with your first answers. If we let w = sqrt(k/m), then frequency is calculated from 2 pi w. The next two answers are correct, which is interesting because if you got the frequency wrong I would expect that these others would be wrong as well.

Given that max velocity is V= Aw, and w is proportional to the inverse square root of m, if you decease m you get a larger value of w and hence a larger value of max velocity.

The graph question is a bit of a trick question. Given a displacement function of x(t)=A sin(wt), take its derivative to get the velocity equation v(t)=Aw cos(wt) and the second derivative gives a(t)=-Aw^2sin(wt). Can you see now how acceleration elates to displacement?