All of the above!
But if you want a "business" angle and to make money sure I can help you there. Question is do you want to make money and it be a painful process or do you want to make money while doing something you are interested in?
First let me introduce you to a game that is a success in the H-game industry, "A Wife and Mother" here on F95. Some 6500(+) pages of fan comments and criticisms. It's just an example I can easily call off the top of my head. That is your bench mark you ought to be aiming for. People call it interest and popularity, think I-phone verse Android.
Tools you will need is first and absolute is commitment to your project. Second, you will need talent. And third you need a team. If you are a one-man band, like in the above forementioned game, that size of a project may make you abandon it because of just the size of it. Honestly, I'd love to write for a developer who has plugged away at the same game by themselves for the last five or six years as in the example.
The game itself. You could go for the market approach as to the genre of the game as to what is popular, but any short coming in the above required tools then expect failure. In the beginning you are going to need to come out of the gate (the start) with lots of content. I have seen so few successful "pilot" games gain any kind of following that a project just dies. Your first release of your game has to be "clean" of any defects in plot, story line, art, functionality, and free of glitches. It's hard to overcome defects since it will taint the whole project.
Marketing of the game is huge to make the startup worth all the effort. If you put up a class-A project and no one knows about it, why even bother in the first place. So you will need some catchy packaging to grab the eye of someone browsing the genre you are in. Word of mouth here on F95 and other social networks will get you almost the fan base you will need to take off running.
Lastly, you, yourself is the key to success. Don't be afraid to recruit or seek out those who can help you. But be able to spot BS when it shows up. Remember if you are serious, your name and reputation are your currency to those that want to help you or work for you. Your work is your brand, and the brand is everything when it comes to income generation. Make a great game and people will seek out other projects you have created in the future. The hardest part is just being willing to work your ass off. First impressions are the worst since it's so hard to fix a bad first impression.
