Spawning at a random position away from the player

You can use Random.insideUnitCircle which would be almost the same as using Random.onUnitSphere and just cancel out the y-part. When you normalize the Vector it will have a length of 1.0. Multiply it with your range and you got your point. This method have a little problem when insideUnitCircle or onUnitSphere returns 0,0,0 which is possible.

Or do it the traditional way: using trigonometry ;)

 // C#
 // get a random direction (360°) in radians
 float angle = Random.Range(0.0f,Mathf.PI*2); 
 
 // create a vector with length 1.0
 Vector3 V = new Vector3(Mathf.Sin(angle),0,Mathf.Cos(angle));
 
 // scale it to the desired length
 V *= Range;