Build Unreal Engine terrain based on a 3D mesh, please see attached files

I got a terrain mesh with textures done in a modelling software and I want to turn this into a Unreal terrain (let me know if you disagree with this workflow, in other words, if I am perfectly fine with leaving the mesh terrain as a static mesh).

In my understanding, Unreal builds terrains/landscapes as a height maps rather than a mesh.
How should I approach this if I have a mesh reference? I can create a heightmap by assigning a gradient texture and render it out. Is this the way to do? Are there other ways?

What about the size? I need it to be exact the size it is modelled.
What about the Z location? It needs to be correct in Z location, so that when I start exporting environment assets, they need to match. No need for millimeter precision, I can move up the terrain object (“actor”?) manually if possible, and if this is the right way. Although, I prefer to automate things where I can, in other words, if I can import it to the right place directly, then I would like to know how.

I do have a texture map; the one provided is 2500x1500 pixels and I got one that is 25000x12500.
Can I project a texture (planar map) to a terrain? If not, what options do I have; vertex colors? Other?
Initially, I want to paint textures in Unreal, so what I might need is probably only a reference so that I know what is where - do I have to place this textured mesh as reference? A textured plane as reference? Another way?

Thank you for your patience for so many questions at the same time :wink:

Please see the attached files (there was a size limit, so here is a dropbox link):