You basically want to get the tips upgrade in the restaurant as quickly as possible (second one), after you have bought the ingredients in the morning that is. While in the kitchen, where you can find the shop button(top left, gold) to get the ingredients and the menu button(bottom right, blue) for the making the meals and getting new recipes, you basically have to make the same number of meals according to the number near the green person icon to avoid spoilage. If you accidentally make more than the number needed, you can just type a negative number when making it to reduce the number and the ingredients will come back. This game seems to have a reservation policy and the customers just get the meal during opening hours, though there are ones where they just suddenly visit and order, it rarely RARELY happens (it only happened twice during my first play-through).
Also, the role selection seems buggy that when you load a save where you have all three of them, it doesn't load the other two icons(bell and yura) and only luluwa is the only one there, to fix this, I found out(the hard way) that you have to load a save where you first got them to work in the bar for the icons to appear back then load back to your latest save. Also, don't try the skip button on H-scenes because it will cause a crash.
For the heart icon on top of the customers, just click on it and the one in the counter will go to the customer and "service" him, which will have curtains if it's ongoing. If you want to view the "service", double click on the curtains and you can control the actions of the "service" from there, remember to exit though 'cause the store is still running in the background and you don't want to miss those tips(coin icon on top of customers) cause they add up, and after you upgrade the tips, it will go from 50 > 75 > 480 > 800 > 2k+ > 6K+, which is obviously better than just doing the meals and the probability of the tips increases in each upgrade, for the meals, having all the 150 price recipes and below are enough, which will give you at least 50 customers, though make sure you have enough money and ingredients for the other meals before you learn a new one.
For the furniture, just get the all the stools and four tables, then all mattresses and after that, anything you want as long as it's not sticking close to the seats for it will block the customer ai, which makes it that they can't order since they can't seat or go to the counter, also, give spaces between the seats(stool and table) so that the ai won't bump into one another resulting in a block.
That's all I found out about the game, hope that helps. I still don't know what's the criteria for the affection meter since I only got the bell ending and it seems to force me into that one.
Also, there no NG+, though it's easy enough to not need one, but still.