My Suggestion :
When you want to create a Private League it will be great if you can have an option to invite managers without their own teams & instead giving all of them exactly a same basic roster with different player names.
During the season they can train their roster the way the want.
This way we can start a tournament with the same chance
Suggestion belongs to suggestion forum. But question for you, how many teams would play that competition? Which way they would be chosen?
If you are a great manager you probably should know that even with good minutes handling you cant be 100% sure about your players GS stay at 9.
But if you manage the minutes well & train GS then there is no need to be worried.
If you have long-term plans not just short-term for one competition it always better to train something else. And it looks you have such a plans, so I try to tell you don't underestimate your chances even without GS great team can make great things.
Maybe once or twice in B3 playoff GS training could be enough for really tough games and mainly if minutes unluckily aren't handled well. Who wants to win the title should be able to beat almost all the opponents without GS training. Difference between very high 8 and 9 (which is always 9.0) is marginal.