Material on FAB

Hey,
I plan to create my first material for sale on FAB.
1 - In my understanding I need to create a PBR texture set, create a material in Unreal and turn it into a pack. Am I correct?

2 - How to create materials variation user/customer can pick from? If the base texture-set is in 4096x4096px and 16bits PNG, how to offer lower quality like 2048x2048 and 8bits for non height textures? Should I create set of the same materials in lower resolution manually and call them somehow, or does UNREAL/FAB does that automaticaly within the same product?

3 - what is the best texture-set setup for everyone? Individual map for each channel? So file for normal, file for albedo, file for roughness, file for metallic, file for ambient occlusion?

or a packed one with file for Albedo, file for normal map, and file for MetallicRoughnessOcclusion stored in its individual R+G+B channels?

I am good when it comes to texture creation but dont know Unreal very well, hence question.
I would really very appreciate any help as I neved did any matereials in Unreal before and just started learning Unreal.

Cheers!
G.