Terrain or Mesh?

Hey guys, I have a question on what to do/best practice:

I have a neighborhood I need to create in Unity. The issue is that I want to take advantage of Unity’s terrain tools (the ability to paint trees and grass/foliage as well as the textures). The problem is that the sidewalks, driveways, gutters, and roads aren’t “painted on” unto the terrain, and instead are separate meshes.

The reason this is a problem, is because I’m not sure what to do with the parts that are made up of grass. Having Unity terrain underneath the mesh and just “raising” the mesh is problematic, because now I have to have a huge heightmap resolution (2048), just to make it granular enough to stick up in the areas that I need. The image below may provide more insight as to how I broke up the work:

So the blue part is where I have issues. Should I create a mesh so that I can reuse it where the grass should be? Issue: No paintable grass.

Should I make a terrain with large heightmap to "raise up " the terrain in those parts? Issue: Non-existent baked lighting, unusable for some reason, and hard to “raise up” just right without poking through some other meshes.

Any insight would be great. My main background is as a 3d Artist.

Thanks in advance!

Unity terrain is a mess.You cant control sculpt terrain for those areas effectively.Create a general heightmap once you finished with the mesh related map topology and put heightmap generated terrain under the meshes then seed and grow.