On collections, I tend to think it's best to wait until you can create a collection that isn't a mixed lolly bag. You know the type: you get them at Halloween or at fairs and they have maybe one or two lollies that you want to eat in them, but the rest run that range of mediocre to shit. There's no set time frame for that, of course, but just because you can get published doesn't necessarily make you an interesting writer. Publishing from story to story doesn't, at least to me, make you very interesting at all, but when you consider your work, and it occurs to you that you're creating a body of work, with themes and concerns and styles, then you're at least starting to become slightly interesting.
I also do think that you can give an author too much early on. It's rather like when you find a child who is a genius, and you tell them, day in and day out, that they are a genius. Soon, they're going to believe that they are a genius, and the results from that are mostly damaging, I believe. You can't think that everything will come naturally, that everyone should love what you do, that you'll never encounter any resistance, and expect to be interesting. And that doesn't even begin to approach that fact that there isn't any real kind of genius, especially in authors. Being able to write one way doesn't necessarily mean that you can write the other way. Can you write a good fantasy novel and then a biography? A lot of authors would tell you they've no interest, but there are different skills to learn for writing each. So, yes, I do think you can give a new author too much, too early. A little bit of struggle is good for the head, I reckon.