As for your other question...
I really don't know how the internal density of the planet will vary with mass, that sounds like a Podquestion. Different minerals will compress differently under pressure, and possibly undergo chemical changes or phase shifts, and I know the earth has a heavy nickel-iron core with a much lighter mantle, so structure plays a big role. I once remember seeing a graph of planetary radius as a function of mass, I'll see if I can find it, but that also makes an assumption of homogeneous internal structure, and I don't know how realistic an assumption that is. So I don't really know if the planetary radius I calculated from your specs is even physically possible.