I know what you mean. I have been helped so much. So, I like giving back to the online community. I started making video tutorials to spread the knowledge, but, after hundreds of hours to finally get software setup that worked, my computer died after only 3 tutorials. But, I like posting on here until I am up and running again.
You need a very high poly count for good displacements. And, the details in a model require much higher polygon density than the rest of the model. If you want that same level of detail on the entire model, the final poly count will be extremely high. But, that isn’t necessarily bad since the poly count needs to be high for the displacement. But, you don’t want the detailed areas to have an insane amount of vertices just to get a reasonable density of vertices in other areas.
This sounds like a perfect place for the remesh modifier. But, the remesh modifier destroys the topology. Even something as simple as a smooth edge is destroyed by the remesh modifier. However, you can make it work to a degree. First, you need a clean mesh. Don’t have intersecting polygons. And, you want to have only one piece, no islands. Next, you need the remesh modifier set to “smooth”, and you need to use at least level 8. You must remember that the remesh modifier could cause shading artifacts, especially on animated models, due to the trashed topology. So, this really isn’t a good solution for many cases.
In practice, you will probably want a displacement map for larger surface variations AND a high-res normal map for finer details. For the larger-scale displacements in a case like this, you wouldn’t need as much geometry. So, you can avoid the remesh modifier. I suggest modifying your mesh’s topology by hand, adding more geometry where it is needed. But, the regular subdivisions would hopefully be enough for this.
Now, you will want a normal map. In the nodes for your material, load a bump map (or displacement map) into an image texture node. Then, connect it into a “Bump” node (found in Vector>Bump). Put the output of this into the displacement socket of the material output. As of the last time I checked, the displacement socket is actually a normal map input, not actually displacement. But, I prefer to connect the Bump output into the normal inputs on the shader nodes.