aminhanifm
Layout loading:
If you join a room after layout has been loaded, the "finish" signal would be "on actor join" event. You can simply check the current number of players in the room in this handler.
Latency:
To measure round trip time to the server, send an event to yourself (specify client actor id in TargetActors).
The same works for rtt to players. Send and event and reply to it back to sender.