Making a MoodBoard for my Year-Project

So, this is kind of a mixture between medieval and high fantasy, there is some environment work as well as armor concept design.

Well, it would be easier to help you if we had some of your work to look at, but I'll go over what you generally need to create these things. As for the armor, you should research medieval and gothic armor (or whatever you need), you need to look into materials and texture, you don't necessarily need to learn poses, but it would help to understand human anatomy a bit, and keep in mind that the body is round when creating these still frame concepts, you should learn some basic design principles, (such as the 70/30 surface detail, less is better, shape language, color theory). Again, it is difficult to help when I do not know what you have yet to understand.

As for the environments, I can't help you a lot there. Keep in mind atmospheric perspective, general perspective, proportions and textures.

Very good advice from @achronic.
Be sure to also look up real armor and real landscapes to understand how they work - referencing only artwork gives you limited information, to paint something properly you need to understand how it works.

As to how to work, make sure you do thumbnails -> sketch (es) -> good values and colors -> then details.
If you jump right in and start with painting and detailing straight away you will run into problems later.

I do this kind of thing a lot for each illustration I work on. I probably know how you feel seeing all the cool artwork images out there. There's so much you like and you hope to capture certain qualities of each image in your own artwork. This is definitely a good idea. But I would make sure you keep it a more narrow focus. For example, your armor sets have types of armor materials. You have metals and some leathers, swords and arrows. Drawing from too many sources can confuse the design and slow your progress. Focus down on what you want to do. Same thing with your environments. You have some very green scenery as well as frost cold environments. Decide what type of environment you want and then only look at those kinds of images to help the mood. Hope this helps!