Is it possible to have different materials (or layers) showing up on different cameras? For doing effects like an IR-camera mounted on a players weapon, or a scanner device held in the players hand. I would like to have the player viewpoint showing the “natural” first-person look of the level, and within that view, have the players hand carrying a device with a screen which shows an entirely different view of the level. A few quick pointers in the right direction would be really appreciated, I am very new to materials and post processing effects in general and just need to know the general direction in which to proceed 
post process effects maybe? try to look them up in content examples
Can you be a liiittle more specific?
To access postprocess, find (or create) PostProcessingVolume. Make it unbound to affect full scene. What you want to do is look at the volume’s properties, more specifically Blendables. These allow you to add a chain of postprocessing materials where you can create all the mentioned effects above. At the start, I suggest making one postprocessing material with all the effects and then choose the effect based of a material collection paratemeter that you should set in your character blueprint. It is not really easy to set parameters to postprocessing materials otherwise.
Look at the content samples on how to make the postprocessing material. Basically, you set the material type to postprocessing and then obtain write the output color to emmisive material property. Based on the effect, you will probably lerp between different colors/maps based of the material parameter held in material parameter collection.
The other (more performant) way to set this up is to add blendables for each weapon effect dynamically to the postprocessing volume(s)