Sometimes it is important to include the radii, especially if the sharp corner creates a stress singularity. In general I start with no radii and only add them when required. If in doubt, a mesh convergence study can help identify singularities.
Actually from what I know of your application a first mode natural frequency of 14.5 Hz is pretty good. This is quite a stiff structure. I was simply pointing out that a frequency analysis can be used to find the most flexible part of the structure.
If, for example, you had designed the structure without the diagonal leg braces, the maximum stress under load, in a static analysis, would be no different to what is is now. But the first mode frequency would be be much lower (e.g. 1 Hz). Intuitively you knew to add bracing in this direction even though the static stress analysis does not require it. In some cases the required bracing is not so obvious. This is where a frequency analysis can help.
The required minimum natural frequency is highly dependent on the application. If the structure is subject to large cyclic loads and good dimensional control of the structure is required then the first mode natural frequency may need to be as high as eight times the frequency of the applied load (rule of thumb).
Sometimes it is important to have a low natural frequency. For example, earthquake resistant buildings are designed to have a low natural frequency. During an earthquake the structure will move large amounts and non load bearing members will intentionally undergo large plastic deformation to absorb energy. If the structure is too stiff it will fail catastrophically because there is no capacity to absorb energy.
If, on the other hand, none of these factors are important then the minimum natural frequency becomes a bit arbitrary. You have to look at the frequency and shape and make an assessment about whether or not you think the structure is stiff enough in that direction.