It's probably already stated before, but if you want to make money, you have to gear up your girls - and not all items have the same usefulness depending of the girl who use it. In a way, the hard mode is easier than the easy mode. In easy mode, the trap is that you will buy multiple girls before you are ready and then go bankrupt because they can't earn more than your cost. Get one, train her AND gear her up. Once she rack more money than you spend, THEN take another one. Having less girls also means more fans, who will leave really good tips the next day. (So you need to nurture those fanbase. The more you serve, the more you get)
the same base chick who rack 22 : 10 - 15 will rack 500 : 800-1k and more when properly geared / lubed.
(if you haven't figured out, the first number is what you get upfront, the tip part is what you get at the start of the next day, depending if you have reached the client requirement or not. The tips don't seems to be properly checked in the sorting, so check well when you pick a client... )
DON'T try to raise obediance from 1 naturally, you'll never get close to 20 without an ungodly amount of grinding. Buy a collar, popper up the girl to enough arousal and equip - arousal can go above the limits and it is the key to everything. Now her base obediance will be enough to do all job and obediance will raise up faster until you reach a point where the colar is no longer needed. Then remove it and replace with something else if needed.
For early game arousal, check the lube consumable that reduce it and your girl will not take 2 days break for each time she take a customer. It's better to spend 3/4 of your gain spending for it than having your lone girl only working once a week.
Once you realize that you NEED the consumables AND the items, the game loop kick in and then the money start to fill the coffer. This is a game, not a slide show. It's not buy and forget - you need to manage the girls arousal and your stockpile.