I would recommend starting with Elm. The language is much smaller, and the error messages are best in class. The error messages from the Glasgow Haskell Compiler (GHC) are often intimidating and it takes time to get used to them. Whatever you learn in Elm will translate more or less directly to Haskell.

Yes, because of the more mature literature and ecosystem. There is a reason quickcheck didn't come out of purescript.

They have vastly different use cases. Elm is a frontend language while haskell is a backend one. You may want to learn both for making a full stack app. Or just learn Haskell and use its wasm compiler.

Even if you want to learn Haskell, learn Elm first. Two weekend of Elm will do more to explain Haskell do you than just about anything else.

Elm is beautifully simple. And it gives you such a solid foundation to learn Haskell and how to think in Haskell. Even if it's not Haskell and is a much smaller language.

4 out of 5 people will learn Haskell faster by learning Elm first, than by just focusing on Haskell. And I mean even accounting for the time learning Elm it still will be faster to learn Haskell.

Purescript is almost Haskell anyway. I love writing it, but it probably makes more sense to just learn the mother language first, since so many more educational resources are available.

Yes, Elm ignores many of the more interesting and important aspects of Haskell for the sake of appealing to JS devs. Go Elm if you want a ML based framework for web clients, but for actual language study, go Haskell.

EDIT: Seriously downvotes for that? Go watch some of Evan's talks on Elm, when pressed for why he doesn't implement some of Haskell's more out-there features, he states that his goal is not to appeal to Haskell devs, but to JS devs, and that he wants to keep the language palatable to them.