That is correct, there is not one simple equation to solve for your spring frequency.

Fact is there are a series of equations and lots of variables in solving sprung mass damper system, along with compromises that are made so that the selected setup is suited for what conditions the car experiences the most. Although it should be able to manage worst case weight transfers or jumps, that may only be one very small portion of the track and may be a benefit to tune to what the majority of the track is instead because it will result in faster lap times.

When determining spring rates you need to know the wheel rate as well which is the ratio for a given movement of the wheel and what that is equal to in movement on the shock (This is where the shock angle/ position is taken into account). Once you know this it is just dependent on gross vehicle weight, tire width, power to weight, track (grip) and a few other subjective variables like driver preference and technique.

However, I think the best/ quickest way to go about setup is to just drive and test and try to run the softest rear springs that will keep the car off the track a the ride height you want. Then tune oversteer/ understeer with front springs and comber link locations.