Maybe you don't display it as an "account", but I can't think of a single commercial website where you shouldn't at least be taking an email address as part of the transaction. Yeah, users love to complain about registration, but I can tell you from direct experience that they love to complain even more loudly when they have a problem, and you can't find a history of their transaction because they never gave you a way to identify them -- I can guarantee that they never printed out your transaction record. Account-less purchases will have their way with you. Don't do it.
As for the rest of it, maybe it makes sense for you to provide OAuth options; maybe it doesn't. It really depends on the domain. Likewise, maybe it makes sense to offer "traditional" login, or maybe it doesn't (Tinder seems to be doing okay). The password advice is good.
Developers are this unique audience of people who have -- well, let's say "highly evolved" -- expectations about how web businesses "should" work. Most normal people don't share their expectations, so don't make assumptions without direct validation from your target audience.