I’ve been searching but I cannot find any information about GM stats or how they work. So, how do they work? Is there any reason I wouldn’t want to max out my GM’s stats at the start of a league? Do they only affect AI controlled GMs?

Also, second question. Is there a way to sub in a specific player during a game?

Feel free to max out the ratings... if you want a challenge in the future reduce them a bit. Up to you.

For subbing specific players, the only way would be to create a specific package with that specific player and use that package.