On the new scene, place your player prefab where you want them to appear and when the new scene is loaded they will start right there.
But returning to the last scene and appearing in the last position takes some work. Easiest way would be dublicating the first scene WITH the player in the phase gate position, but it’s not practical if you are planning to place a lot of gates and you will have a lot of levels.
There is also a command called DontDestroyOnLoad()
You can store the last position of the player in a variable, and when you turn back to the first scene, you can position the player using that Vector3 variable in Awake()
There are a total of 15 maps in the first galaxy. Each one having 1 or more phase gates to take you to different systems.
I would probably only want the starting star system (for each race) not destroyed. Every other system would be fine, based on the previous statement you said above…