Sorry, that I wasn't that helpfull.
When I did my first Unity Assets when VaM first supported them, I had to go through the same like you. Nowerdays I do not create much assets anymore, because it is lot of work and mainly to set the materials. If you have a Unity scene with hundreds of different materials and three time more maps and textures, it is a work of days till it looks good (maybe it is my perfectionism). If there would be an easy way instead of trial and error, I would tell you.
Maps: You can do amazing things with maps like albedo/diffuse maps = textures, normal maps, metallicy maps, glow maps, aso...
Normal maps are for a faked surface structure and therefore only indirectly involved in reflection.
With the standard settings like smoothness and metallic, you can get nice fake reflection effects, that are IMHO good enough for most assets.
If you really want materials to reflect the skybox in VaM in realtime, you have to add a Reflection Probe to the Unity scene. You can find it under Component/Rendering/ at the top of the Unity editor window. Remember that this will cost you a good bit of performance, if you choose the realtime option.
You can "bake -in" an reflection or light map, that is not that much ressource hungry, but that is some kind of fake, too. Maybe that is what Oeshii has suggested? As I said before, maybe you want to check if it is not sufficient to only use metallic and smoothness effects for some kind of smooth fake reflections. Otherwise, it is a bit tough in the beginning.