Mandarin Companion has some educational material for their readers (and readers in general), maybe check with them? A quick search gave me this, for example: https://mandarincompanion.com/wp-content/uploads/2020/08/How-to-Use-Graded-Readers-to-Build-Students-Fluency-Mandarin-Companion.pdf

The idea with extensive reading is that you’re focusing on content where you know as much as possible, preferably 98-99% of the vocabulary. That means you shouldn’t come across that many words you don’t know, although there will of course be some. For Chinese, some of the words you encounter will consist of characters you don’t know, but this is an even smaller percentage. IF key to understanding the text or if you see such characters more than once, I would stop to look up how to pronounce them, or at least save them somewhere for later checking so as not to interrupt the reading too much if you think this is a problem. I sometimes read books in Pleco’s file reader and while I almost never come across characters I don’t know what they mean, I do tap characters often just to verify the pronunciation!

I think it depends on your preferences and personality, but in general, I would say read as much as possible, re-read as much as you like without feeling too bored, and also listen to the books. Repetition is only bad if you find it boring. That being said, if you like studying grammar or vocabulary, by all means extract things to learn, but don’t feel that you have to. The more I learn about these things, the more I favour just more (quantity, extensive reading/listening) over obsessing over less (quality, intensive reading/listening). Hope this helps!

Yes, reading children’s books is usually a bad idea. They are much, much harder than most people think, especially in Chinese. This merits an article at some point, but graded reader are so much better for extensive reading than children’s books. I mean, even some non-fiction for adults is easier to read than fiction for kids. 🙂

The first book I tried to read was “the three little pigs”, ended up with about 60 new pleco flashcards and a headache..
I found some graded readers from Sinolingua on Taobao that I like, collections of short, contemporary stories. Follow the HSK vocab, which I feel is sometimes too formal, but because they’re fairly short can read a whole story before your head hurts.

Yes, intensive reading is better than no reading. Also, it’s incredibly hard (impossible) to find enough extensive reading material before you know a few hundred characters. As soon as you can access graded readers (Mandarin Companion has several on the 150-character level), I suggest you devour them, rather than pursuing ever harder listening material, at least for the bulk of your reading!