Rigidbody physics of scene objects

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Hello everyone,

I am quite doubtful about the best way to do this: I have a spiked boulder with Rigidbody in my scene that can get hit (like a soccer ball or something, but it's big and heavy so it's not really fast ) and i put the usual rigidbodyView and transformView on it for syncing, but I still have some details i don't understand:

1)Who can hit it? For now i have a script with a "OnTriggerEnter" that applies a force to it when the correct hitbox enters it and i only apply the force if isMasterClient is true. So it's like the MasterClient is an "authoritative server" that handles all the physics and then it's updated on the other clients, couldn't think of any better way than this but maybe there is?

2) Since the object is only hittable from the MasterClient, should i set isKinematic to true on other clients to prevent interference from the physics? it seems to work better this way, but i didn't find any guidelines about it anywhere...

3) If i have a lot of these objects in my scene, i suppose the number of messages per second in the room will go up real quick? ( it's a 4 player game, so assuming that the sendrate is 20, this makes 4*4*20 = 320msg/s for the players, and then one networked scene object makes it 4 * 20 = 80 msg/s more? i'm really not sure about this)
Is there any way to cheat this? like having some kind of "props manager" that handles the syncing for all scene objects? If i do this i suppose there is no way around rewriting all the position and velocity syncing code, because obviously i can't just drop a transformView on it and expect it to sync every child objects attached to it or something like this...

thanks for your answers =D