Unreal isn’t really suited out of the box for large scale rts’s.
Some people try to get around it’s limitations with hierarchical instanced static meshes for units.
The ai and path-finding is usually calculated on a custom second thread (you would probably need to program your own flowfield for unit traversal)
As for ai that’s a whole topic on it’s own. You can forget about behavior trees at that scale and using unreal’s built in ai systems.
Collision detection on HISMs is also simplified so you would also need to calculate HISM x HISM collisions.
As for networking Unreals solution is catered towards mid size fps games so with 500 units you will starve your network connection leading to dropped packets. A lockstep solution would probably be a better solution for larger groups of units. (again you need to write custom tech at this point)
If you want a skirmish 2 x 2 for example that’s 4000 unit’s. Totally not possible with unreal’s network based on replication. You would need to make unit movement / reaction totally deterministic and then pass commands to a queue and execute them via an internal lockstep function and then distribute this to players with a timestamp and execute the commands in order.