So how does the level scaling of the game actually work?
How far you progress into the story? How high you level up your characters? How high you level up (You)rself? A combination of multiple factors?

My main team 6 characters reached the max exp level and can no longer attain exp. But my max level is still just level 40 since I haven't bothered to do the rank up trials.
But if I do the rank up trials. Will the game actually become more difficult? And will it become more difficult even if I swap out all 5 of my characters for a different low level team?
Because I want to train a brand new team from the ground up. Will that be more difficult if I level up my OG crew to level 60? Or am I safe to do so?