The description in game is literally all there is to it. There are no deadlines for payments to Mio.Hmm, maybe that can be explained a bit better in the game (even give a warning perhaps)? I finished the game in coomer mode, and that was too easy/simplistic (for me) I guess (and in the end unsatisfying); just set, forget & keep happy (and maybe even that isn't necessary in this mode)
In regular mode, there are and if you don't make them you lose and game over, which necessitates being smarter with your investment strategy.
Coomer mode, as explained in game, is explicitly for those that don't want to have to worry about losing and just want to enjoy the porn, so please don't judge the difficulty of the game based on the literal easy mode.