Let me just start off by saying it's going to be hard to get materials like gravel to look great with textures only, if it's important I'd try to add some pebbles from the Enscape library on top of the texture, or add several layers of pebble-surfaces with cutout-textures.
A good way to get familiar with the texture maps is to check out the advanced Revit materials "replace this asset" in the top right of your image.
Looking at your image, first of all whatever looks good... but If we are picky the correct slot for DISPL(acement) is actually Relief Pattern and if you'd rather use a normal map (like you have) you should click the normal map image and change Advanced->Data type to "Normal map".
So basically DISPL and NORM does the same thing, I've found normal gives a bigger effect but the "depth" doesn't seem to be controllable in Enscape (pretty much on/off)
In Roughness there would usually be a ROUGH map, but honestly this way probably works fine especially if there is no such texture, if you want some extra control over the "shininess" of the material you can click the image in the slot and pull down brightness to make it more shiny (dark = shiny) or do the same thing with an external image editor if you need it less shiny, or if it's not a very shiny material you can just use the slider.