The balancer is likely to be no worse due to the three missing bolts. If it was already slipping and squealing when cold and first started, it will still slip and squeal. If it wasn't slipping immediately before, it won't now. (But for how long until it does? The original design ones all will.).
I'd replace all four of the bolts and then only replace the V pulley if it shows signs of lateral movement as it rotates.
The crank snout is also likely to be OK. Don't create a problem (one you DON'T have now) by re-using the crank bolt.
For peace of mind try to tighten it with a torque wrench set to about 80 lb*ft. Normal is 66 lb*ft + 1/4 turn more. 80 is less than required to get that additional 1/4 turn so you won't over tighten and weaken the bolt any more, yet over 66 to assure that it isn't too loose. If it moves at less than 80 someone has been in there and not set it correctly. THEN, if that is the situation, replace the bolt, check the crank, and consider replacing the sprocket.