Ran some 20K tile maps without trees and it was pretty good. Hard to say how much lag there is because at high altitudes moving around is naturally slow, but definitely better than it was with trees. Trees might add 50-100K meshes to my scene. I am thinking under 30-50K meshes is manageable, but that is also going to depend on what texture resolution, how complex the meshes, etc.
The math we were talking about is really on my end since I could Get from an array or do 3 steps of math to get the same value. He said that the math would be more efficient since it could stay on the CPU and not access memory, in addition to it trawling the length of the array.
I think you should be able to process some pathfinding information in the background between everything else by using a tick function to space it out based on performance. Then anything leftover could be worked out at the end of the turn. I don’t know exactly how that would be done, but from other discussions it seems the way to go, perhaps even in C++.