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@protonhorse
Very welcome. Unfortunately, there is no tool that works imo, even though there are a lot of tools that claim to be able to to realistic vehicle handling, they cannot adjust for the randomness in center of gravity/balance on vehicles. Truth is, you have to just go about it the hard way if you want it done right, set the forward/backward bodyroll, set the side to side bodyroll, then you have to guess at the positioning of the center of gravity of the model and adjust it if it is too far forward, too far back, and/or too high, or too low. As for setting the classes etc, I use low wind resistance values for less impacts/suprises in racing and police chasing etc, and for fairness in racing and police chasing, I usually use the same wind resistance and acceleration and top speed values within a min and max for each class.
The other thing is, you just have to guess to a degree with your value changes in the handling.meta, but knowing what to change based on how the car feels, and how to get the vehicles all to a place where they are fair within their class is something that just takes a lot of time and trial and error. Honestly, it can take anywhere from 5 minutes up to several hours to get a car "just right"

As for the classes and speeds, you can look in my handling files and see what I did, and look for the differences in each class and go from there. I wish there was some easy trick to it, but there just isn't, good vehicle handling is at the mercy of the center of gravity of the vehicle, and the abilities of the vehicle dev tuning the vehicle. If the center of gravity is too far off, the vehicle is a write-off for the most part, best to look for a replacement model that does not have bad center of gravity issues, as there is only so much you can do to fix the issue without making it perform poorly in other aspects, to the point where it will not even be able to race in its class.