I think we're all better off going with the opinion of the SDNY than hacks like Dershowitz.
https://www.documentcloud.org/documents/5453401-SDNY-Cohen-sentencing-memo.html
Stormy tried to sell her story to the National Enquirer. The chairman contacted Trump's team, said, hey, we got another bimbo eruption, you guys need to handle it! So they did - buying her story with an NDA. How is that extortion? If Cohen had done nothing, she'd have simply told her story, which she's entitled to do, for money or for free depending on whether bottom feeders like the National Enquirer believe her story is worth paying for.
BTW, Avenatti didn't get hired until well after the NDA, so your timeline is pathetically wrong.
And the crime isn't that Trump paid her off with his own, personal, funds. If he wasn't advised by idiots perhaps that's what he would have done. Instead, he had his fixer (Cohen) pay off Stormy, then ran that bill through his companies as 'legal expenses' over the next year or so. And Cohen cannot legally make campaign contributions on behalf of Trump for $150,000, and he sure cannot do it without the campaign disclosing the contributions. Also, companies cannot make those kinds of contributions either, which is what Trump's companies did by paying off Cohen's illegal contribution.