DCY, I think you might have gotten a bit ahead of yourself here. The ability to evaluate different developers is based on the assumption that the negatives are correctly exposed. Based on what you have said, you have not yet achieved a complete understanding of the camera and it's light meter.
I'd take a step back and learn about light, and how to meter it. I'm not meaning the Zone system and all it's variants, I'm thinking of basic use of a light meter and it's limitations, such as you discovered with white sand. Once you have a complete grasp of how your camera meters, then you can understand what to do with the reading it suggests and when to use it or not. You'll learn to recognize the situations that might call for a different metering technique.
Then you can move to learning about exposing film (the Zone System is one method, there are many others), and then once you have mastered metering and exposing, then move onto developing.
There is no point in trying to perfectly develop a poorly exposed film.
I know it's been said before, but I would use one mainstream film and one developer for the metering and exposing phase of learning the craft of photography. The reason is simply to control the number of variables. I would probably also stick to a commercial developer, whatever you choose, and strictly adhere to the manufacturers recommendations.
Also best to use the same companies film and developer. They know the products, and they want you to succeed; they are not going to make recommendations that don't work.
Once you have mastered all 3 aspects (metering, exposing and developing), then experiment and make changes to your hearts content; but you need to have the foundation under your belt before you can make any meaningful evaluations of the results of your experimentation.
I am assuming in the above that the end goal is nice looking prints, rather than the experimentation being the end goal.