You can assign your Materials with polygon selections in C4D.
If it doesn’t import correctly to UE4, check your export and import settings if the export and import of Materials is enabled.
Depending on your C4D Version, fbx Exporter Version (v6.10 works best in most cases), export settings and import settings, you might have to import and assign the Textures manually.
(I think it was R17 with fbx 2010 v6.10, which imported Textures and even applied a TexCoord node if your Material in C4D was tiled by using the U and V tiling parameter of the Material)
However, when creating Models for Games you have to take a quite different approach to texturing then you would do for rendering.
Usually your aim is to use as few Materials on a Model as possible.
For most Models this means one Material, but for some others it’s better to use more.
(e.g. a Tree which has a tilable trunk Texture and one for the leaves that uses alpha channel for transparency and maybe even disabled backface culling to render both sides of the leave planes)
When creating textured meshes for games, the bake texture Tag in C4D will become one of your best friends.
You can start off as usual and assign a multitude of Materials to your Model, but then you bake all these Materials into texturemaps that can be used with a single Material.
Ofc. you’ll need to have a good UV layout done for that mesh, otherwise it won’t work properly.
Sadly not all Material parameters and effects are bakable and some need workarrounds.
But once you got some experience with it, you will start building your Materials with baking in mind.
Another possibility, maybe the preferable one, if you have Substance or Quixel, would be the creation and baking of a colorID map which can be used for texturing in these apps.