Hm, If you let your application handle 1000 Entities, there
is something wrong with your approach.
You should only handle entities, that are relevant to the gameplay and!
are not static, and cant be predicted by the client.

So controlling an NPC that can attack players is ok, controlling a "lightingbolt" model
over the net is not ok.

A lot of entities can be purely controlled by the client. Every entity that does not move, and
every entity that will not interact with the player/s (like a bird circling in the air).