The budgie is fully feathered and then try to comfort both bird to see if they like each other. Do not rush things.
Bigger birds often kill smaller birds. I don't know if Bourkes will kill budgies but I wouldn't risk it. Keep them separately caged.
It depends on the bird, however many larger birds are capable of killing a smaller bird. Also, many birds are capable of killing another bird of the same size.
Never trust any bird not to hurt another bird. It happens all the time.
