The game is as easy as it gets, I really don't know how you couldn't double the target amount. Why so many pages about cheats...?
The girls "problem missions" early on are the only hard thing, but most of them come down to "Aim at umbrellas" or "Wait for a truck to bounce against" really. The girls start with enough stats to take care of the missions themselves, just need to clear the trash.
Take over an area, attract customers until they're gold, repeat with each area. Buy all the interior stuff, unlock the good massages then start leveling them up once you have 5 phases for each and you'll have so much money there's nothing to use it on outside of maxing stats for no real reason like 15 days before the ending.
Which is where the greatest problem of the game comes in, there's not a whole lot to actually do once you have the management finished.