By the first I meant that I would prefer to do some model work myself, e.g. a deployable Dispersion Pistol (the one LPS uses has no support for that) or the classic Na Pali palms in better quality. I don't think I need textures though as I can quickly remake whatever I need and already did so (screenshots will follow in an update post for Vortex Rikers soon).

Since detail-textures are no more an option as back then, you are best off having 2 normalmaps and at least 1 diffuse and 1 specular texture.
One normalmap is the overall normalmap and serves for the rough depth of the texture (structure stuff like the gaps in the platewalls of Vortex Rikers for example), but these will be blurry from up close, so it is best to use a detail layer on top of that (also normalmap) to add tiny irregularities and alike. A bit like noise to hide the blurry normalmap. It shouldn't be too extreme or you got visuals that you get lost in (too much noise affects readability of a map), but a weak detaillayer will definitely do the job. With such a layer, you can visualize scratches too.

Ideally, to conserve the Unreal look, you can take e.g. the metalscratch detail-texture and turn it into a normalmap (there is a normalmap plugin for GIMP which I use and it has proven to be good, however, you have to increase intensity of your generated normalmaps by ca. 3-4 times by layering them on top of each other or increasing contrast, saturation or alike, otherwise it'll be barely noticable). The metal pattern texture on the other hand would make for a good detail layer for a specular texture, etc etc.

You'll have to play a bit with it, but I'm convinced that even with default Unreal textures you can achieve good results, but if you use (let's say) S3TC textures for the diffuse but generated a normalmap and alike from the original (the S3TC would be too noisy to be useful for anything else but diffuse imo), you might have something great-looking there.

Another thing you will have to consider is whether you even want to use S3TC stuff as they already contain "lighting" on them which is more noticable than on the original Unreal counterparts. In combination with a normalmap it might look weird. Again, something you will have to play around with.