I did not see the request for the length. OTOH, I could not have answered that part, at least not without drawing it out.
I have a friend who could work it out on a computer with Autocad. When I need help I call him.
I this case what I would do is draw it out. Big piece of paper or plywood and a compass. Then sketch it from there.
The way I do the angle is 2 the number of sides and divide that into 360.
Don't know if the five pieces is really important to your design, but there is a neat trick if you want six sides. Draw the circle with a compass or tramel and without changing it, "step" it off around the perimeter of the circle and it will go exactly six steps. I'll leave you to figure the angle. (30*)
With five sides, I would draw the circle and then fiddle with the sompas until I got exactly five steps. Then draw in the five spokes and then figure how long to cut the pieces after drawing the inner circle.