Using Blender
Note that this document will not cover the basics of Blender.
Several tools were created to make Blender compatible with modding Arc System Works games.
Modified gltf plugin
Download the modified gltf plugin
Fire up Blender, go to your Preferences > Add-ons. Type gltf into the search bar. If it doesn't show up, make sure you're in the 'Official' tab.
Disable it. Nuke it. Throw it out the window.
Now close Blender, and extract io_scene_gltf2_ue4.zip into your Blender addons directory.
For Windows, this can be found in:
%appdata%\Blender Foundation\Blender\ <your Blender version> \scripts\addons\
Next, fire up Blender and go back to the Add-ons menu. If all went well, you'll find a new entry in there called Import-Export: glTF 2.0 format - For Unreal Engine Modding. Simply enable it, and you're good to go.
You can now import gltf meshes & skeletons via File > Import > glTF 2.0 (.glb/.gltf) - Unreal.
Aerthas' custom materials & shaders
Download BLENDER-Arc-System-Works-Shader
Not strictly needed for modding these games, but superb for preview models and textures within Blender itself.
Aerthas made a ton of practical videos on how to actually use his shader. Although the YouTube playlist is linked on that very Github page, don't mind if we link it here as well.
Scripts
The most useful scripts have their own wiki pages, which also go into detail on how to use them.
A note on Blender FBX export into UE4
Vanilla Blender FBX export is kinda icky. If you're willing to pay up, consider Better Fbx Importer & Exporter instead.