yes g_spawn error will appear when you reached around 1022 entities (exactly: 1024 I guess)
Maybe will also help to use spawn method on the triggers, origins, models when it is needed.
like you can do spawning a EE after amount of rounds that is survived or also possible option is maybe to do a EE in steps like as example:
spawn the EE after round 5 for step 1.
finding 3 different keys to unlock a special door.
when they finished step 1 and have unlocked the door.
you can spawn step 2.
you need to find some items to build and use it somewhere else in the map.
it is a suggestion
Sorry for my bad english.