When Patreon started its ban over incest, bestiality, none consensual sex, and underage content, a dozen project for an alternative platform were started. A this time, a bit more than 6 years later, none of them exist...
As others said, you need way more than just build a website for this kind of project. And if you decide to use crypto as sole currency, everyone, both patrons and creators will expect a fair price. Therefore you'll have to have price expressed in US $ (or whatever), ensure that the portion of BTC (or whatever) you'll take will correspond exactly to this sum at the instant you take it, and immediately transfer it to the creator wallet; possibly minus your own fees. And of course, you'll need to have enough credibility for people to trust you on this.
And, something that haven't been said yet, you also need to know a really good lawyer...
You want to create an platform that will serve as intermediary for financial transaction about material that is considered as illegal in a big part of the world, when it's not the transaction themselves that are illegal; there's countries when you can own [this or that] but not sell it or buy it.
It's obvious that soon or later the authorities will goes after you for complicity in a crime, and facilitating it. Like the transaction would probably never have existed without your platform, they would probably also add incentive to commit a crime to the list.