It sounds like you’re already using a lot of optimization techniques, which is great! Are you actually encountering any performance issues?
As far as where you could optimize even more, material slots can be a big one, but only if draw calls are an issue. The best way to think about material slots is to separate them out by material type- not texture type. If you have an object that needs an opaque material and a masked material (the most common example being a tree), then this asset needs two material slots. If the only difference in material slots is the texturing and maybe some small effects, you’re better off combining these textures. If you have two different effects in one material, it’s common practice to replace the Metallic or the AO (whichever you need less) in your ORM map with a mask between the two original slots, then you can use that mask to determine the differences.
Less of an optimization and more of a heads up- Lumen can’t use stationary lights, this is a very common misconception. Stationary lights are a mix of baked and moveable lighting, where you can bake the bounce of the lighting into the lightmap but then still change the intensity and color dynamically. Since Lumen removes the use of baked lighting, it just turns stationary lights into movable lights. To save yourself any confusion, I would recommend just switching those lights to moveable.
That’s a great note on the emissive texturing! Yeah, from my understanding the emissive lighting is calculated by Lumen’s GI so it does not have to do any of the expensive shadow casting.
Overall, it sounds like you’re doing great at optimizing your project. This is a step a lot of people miss, but it’s also the most important, so truly great job paying attention to this.
That being said, are you experiencing any performance hitches? If you send over some information, I may be able to help you narrow down where it’s coming from since you’ve hit most of the go-to optimization methods.