For my Grape vines, I did it all in cross-plain style. There is a rectangle between the poles with the base texture and wires painted on, then I did cross-plains jutting out the side for some extra 3D volume.
I would try to make segments of around 10-20m, in my case, I believe I was able to do 20.
Obviously this wont follow the terrain very well if the rows are on sloping terrain, so some manual rotation may be required in the sim (Setting Gizmo tool to use Local at the bottom helps make this a little less painful), or just shorter segments. However, remember that the less individual models you place in the sim, the better your performance will be, so longer segments when possible is always favorable.
Also, be sure to join your model parts together in Blender (Ctrl-J while over the Object Mode window, with all parts selected) and then run a Merge by Distance (Search for it using F3) to remove any duplicate vertices (default value is fine). Each loose model part technically counts as a draw-call, so that can dump performance and turn the sim into a stuttery mess if you have a larger volume of the model placed. It also goes without saying that you should use the least amount of materials and textures as needed. In the case of my model, I use one material for the poles and another for anything that has transparency. The poles are standard PBR (ALBD, COMP, NORM), while my vegetation just uses ALBD.
As far as the grey/white at a distance goes, I have never found a solution to this.
I have also brought it up to Asobo and they have troubleshooted. It seems to just be an anomaly with textures using transparency at a distance. Pulling your final gltf into Model Converter X and assigning Vertical Normal in the material settings for your transparent texture helps with the shading a bit, but the issue is still there if you're at just the right angle (This will also allow snow to accumulate on the cross-plane vegetation).
Edit: Also, if you are duplicating large amounts or groups of the vines in MSFS, it may be creating duplicates. There is an option under the first tab of the Scenery Editor window (I think that one) that says remove duplicates. It may help to run that as well. Just note, if you did use groups, it will likely mess up the organization of those groups, but the original group you created will stay intact.