PROGRESS! Okay thanks to @HyCraftHD(YT Comments) and @Kaelym searching in the DefaultBiomeFeatures Class did eventually help.
I only got it working for the overworld though so it would be great if someone could fiddle around with it to get it working in the nether/end/other dimension.
I've made an OreGeneration class that looks like this:
I found this OreGen Class by @LTNightshade and edited it so it'd work with 1.14.2
The public static void SetupOrGen() can then be "called" in the setup function in your main class.
I realy hope a dimension implementation isn't too hard to pull off.
GL HF