Which maps should I bring in from Substance Painter?

Elarionus

In the past, I've just used the UE4 materials, or the PBR MetalRough preset, flipping the Y channel of my normal to fix the DirectX and OpenGL conflict. I want to create a new Marmoset Toolbag specific export from Painter.

I personally texture with Color, Height, Roughness, Metallic, Normal, Specular Level, and Emissive (Sometimes Specular as well, which seems to just control the color of it, though that doesn't seem to ever change anything). What maps should I be aiming for in my export? Does it really TRULY matter if I use metalness and roughness in my Marmoset render?

EarthQuake

It's up to you and your preferences. The standard workflows are the metalness and specular workflows:

Metalness

1. Albedo
2. Roughness
3. Metalness
4. Normal

You can also load a secondary specular map, which controls the specular values for the non-metal areas. In Toolbag you'll want to use the Advanced Metalness mode if you're doing this. This isn't necessary for most materials, but may be for skin or certain types of gems. Generally speaking if you need fine control over specular intensity and color, the specular workflow is better than metalness, but it can be somewhat more prone to error / physically incorrect values.

Specular

1. Albedo
2. Gloss (but Roughness is fine too, these are the same types, just inverted)
3. Specular
4. Normal

With both workflows you can add extra maps, like AO, opacity, displacement, etc. It all depends on what the asset needs.

The metalness and specular workflows are two sides of the same coin, the main difference is how the content is arranged in the maps, so you can use whichever you like best if you don't intend to use the asset outside of Toolbag. More info here: https://marmoset.co/posts/physically-based-rendering-and-you-can-too/