moving random objects to random positions

Something like this is what you are looking for, or should get you started, I think:

     // Loop for each object, minus 1 because the last one we will duplicate so we have 2 of the same.
     int count = 3 + (2 * LevelNumber);
     for (int i = 0; i < count; i++)
     {
         // Pick our random object type
         int r = Random.Range(0, _object.Length - 1);

         // Ugly code loop to handle the duplicate (change this to better syntax/layout)
         while (true)
         {
             // Create a copy of this object type (I'll leave it to you to figure out how to destroy at end of level, if needed)
             GameObject obj = (GameObject)GameObject.Instantiate(_object[r]);

             // Calculate random values for X,Y,Z and set location of new object
             float x = Random.Range(MinX, MaxX);
             float y = Random.Range(MinY, MaxY);
             float z = Random.Range(MinZ, MaxZ);
             obj.transform.position = new Vector3(x, y, z);

             // If this is our last object, do one more of these inside loops to create 1 more of same time.
             if (i + 1 == count)
             {
                 i++;
                 continue;
             }
             break;
         }
     }

Notes:

_object = an array containing your different types of object, just 1 of each object type.

LevelNumber = you'll have to figure this one out, I keep a global variable in my games and update it anytime I change levels, you can do the same if you want

MinX, MaxX, MinY, MaxY, MinZ, MaxZ = you'll want to define these variables or just replace them with whatever min/max values you want for the spawn locations (i.e.-depends on the max size of your "world"). If you don't want one axis to be random, just make it a fixed value.

Please don't use this code as-is, change it to a better syntax, I just like code I can copy/paste as a single part and not multiple functions for a simple example -- plus, I don't like spending too much time writing perfect code for others to copy/paste vs learn :)