Deriving radiance from irradiance and intensity
Your definition for radiant intensity is wrong: it should be just $\Phi / 4\pi$. There are only $4\pi$ steradians in a sphere no matter how big it is, so $r$ doesn't come into it.
Also note that you can't calculate radiance for a point source—it would be infinite, due to the fact the point source emits a finite amount of flux compressed into zero size. It subtends zero solid angle, from the receiver's point of view, so the $d\omega$ factor in the denominator of radiance would be zero. The usable quantities are radiant intensity in a certain direction from the point source (which could vary with direction, for a non-omnidirectional light), and irradiance in a certain direction and distance. As you've seen, irradiance is obtained from radiant intensity by dividing by $r^2$—you could think of this as &quot;area per steradian&quot;, as it's the conversion factor from $4\pi$ steradians to $4\pi r^2$ area of a sphere; then the units work out.
Where radiance would actually show up is when dealing with an area light rather than a point light. Then you would have the flux being distributed over a finite solid angle from the receiver's point of view, and you'd get the incident irradiance by integrating the light's radiance over that solid angle. The emitted radiance would be $\Phi/(2\pi A_\text{light})$, assuming it's emitted uniformly over the surface of the light and into all directions from each point. This is only $2\pi$ since it's only emitting into the outward-facing hemisphere. Also note that you don't do any division by $r^2$ for radiance—with area lights, the distance attenuation comes naturally as a result of the light subtending less solid angle from the receiver's point of view, when the receiver is farther away.