So you only show one monster at a time? When one monster is destroyed, then the next monster appears?
You can put all these monsters on the layout and set them invisible, disable behaviors etc. Then simply enable them one by one.
Or place spawn points on the layout (invisible sprites). When you need to spawn a new monster, pick first spawnpoint, spawn a monster, destroy spawnpoint. It will still be easier than creating and maintaining that array.
The array only makes sense if you generate all these thousands of coordinates automatically, for example in Excel with some formula, or using some level builder.