Asset size for importing to UE4

What is the best practice when it comes to the size of the assets that I need to create for UE4 (or for publishing in Market place)? The issue is that I have various assets downloaded from the market place and they all appear to be of different sizes, resizing them after importing to UE4 project is a pain and worse it is not very uniform.
So if my work flow is to create base mesh in Blender, create high-poly in Zbrush, bake/texture in Substance Painter and finally export from Blender as FBX to UE4, how do I start with the reference/base size? One approach I have tried is to export the UE4 mannequin and use that as a reference to start creating other assets. is there any best practices that I can follow?

In addition if I am using assets from the store to complement the assets I have created by ‘Add to Project’ is there any way I can scale all of the meshes to a certain scale?

Thanks!

UE4 treats units as centimeters. There’s scaling options when importing an asset as well. Most market places should at least mention at what scale assets are.