Displace aka Heightmap WM -> Unity 3D

hello,

I want to do a proper export of a displacement or heightmap from WM to Unity 3D terrain editor.
So, I´ve read some stuff, but getting more and more confused.

Mainly, I´ve got 2 questions:

To get a useable map out of WM, it is good to check the “+1” option for the resolution, right?
So 513x513 instead of 512x512 for example?

The resolution of the heightmap does not matter, if it is 500ish or 2k ish = the result in Unity should always be the same?
Is there something more to look at, when useing spaltmaps, for example?
I think, I´ve read something like splatmap + displace map have to be the same resolution or something like that.

Please help me out of this !

edit: Ok, from what I´ve found out, Unity need “+1” Setting and the resoulution of the map affects the “pixels per meter” in Terrain Editor - can someone confirm that?
So it would be a good idea to have a 2049x2049 highmap around, if working with it.