Using Auto Rig Pro for Blender v2.90 I have now rigged and skinned this character. It is rigged to the UE4 Mannequin Skeleton. Upon import of the FBX file that came from Blender, I chose the UE4 Mannequin Skeleton for the skeleton within the import options dialog. This skeleton was already present within the project and you can get it with any free Unreal Engine demo content. e.g. from the Third Person Template or Animation Starter Pack for example.
The attached screenshots show the skeletal mesh using the default walk animation and also show the skeleton that is assigned to the skeletal mesh. So this means that no “animation retargeting” will be required in order to use this skeletal mesh with any marketplace animations that are also rigged to the UE4 Mannequin Skeleton (aka the Epic Skeleton).
Next I’ll investigate and implement visually equipping the armour, clothing pieces, weapons and shield. New skeletal meshes will be required for the armour and clothing pieces. Sockets on the skeleton will be required for the weapons and shield. The default rotation and pivot points may need modifying for the weapons and shield in order to orient them correctly upon equipping them.