For problem 4, please plot the line yourselves, using the parametric function and drawing points, rather than using GL_LINES.
For problem 5, you may not be able to see the unit-length perpendicular bisector if your window is huge. Please use a window/coordinate system that is small enough to make it visible.
For problem 6, "clipping" a line segment is formally somewhat ill-defined because I didn't give you an inside/outside function. What I mean is that your algorithm should turn Xs into Vs.
www.voronoi.com's website, which includes a pointer to a nice introduction to Voronoi diagrams and a chapter from a computational geometry textbook that should help you understand how to figure out which pairs of points are "adjacent."
useful link from Andi