So basically, you're saying that duplicating information for every single data on your character would be tedious?
To be honest, I'm also a novice, so I do not know the best way to do this.
On the other hand, you could save data into a file, and then extract the information to be used again. That's definitely possible (but to be honest, I think that would be tedious too).
You could also just get the info using get_node() when the node is about to enter and exit the main scene.
Honestly, I have no idea what to say about this. I do agree with the 'everything as nodes" philosophy, in which everything is contained in their respective nodes. Saves headaches for a lot of us.
If it were me, as a complete novice, I would save information that does not need much manipulating. For example:
If I were to save player data such as health in the autoload, when the player is damaged, I would need to calculate the damage taken in either the autoload or the player scene. If I were to calculate it in the autoload, I would then have to update the player health variable in the player's own scene. If I get rid of the player data as a whole, then I would have to get the information from the autoload, calculate the damage taken, update the variable, and then update the GUI and change the player or GUI behaviour, as needed. Tedious, just like you said.
On the other hand, autoload would be useful for information that would not be manipulated often, such as preferences, like hiding controls during a game, dark theme or light theme, viewport area, things like that.
With data like a player's health constantly being manipulated, I would think it would be better to contain it to it's own node.
With information that you exclude from the autoload, you could also just get the info using get_node() when the node is about to enter and exit the main scene.
Sorry for the long answer, got caught up in writing. Feel free to ask more questions if necessary. And don't take my word for this. If needed, you should probably create a separate question based on this. "What information should I store in autoload?"