I haven’t really got an up-to-date answer, but there are a couple of things to say.

It’s not clear what you mean by zero level. Apparently you can count, and are familiar the concept of zero. It took mankind a long time to invent a symbol for zero. So perhaps basic arithmetic is your zero level. You need to somehow make a map of your task, and the first thing is to establish what you know and don’t know. An old book, Prelude to Mathematics by WW Sawyer is quite a good place to start to get an idea of where you are, the direction you are going, and the kinds of thought processes involved. Concrete Mathematics by Knuth et al, is also a popular foundation.

The only way to know what is involved to reach graduate level is to look at degree courses, at the lecture courses that comprise the degree, and at the reading list for the lecture course. But textbooks cover far more material than a course would teach. The teacher would normally direct you to the parts you need to master. The rest is there to give teachers flexibility, and students reference material that will be accessible as needed after the course is done.

So I’d recommend using online courses to guide your study. You need a framework to hang the individual bits of maths on to, and you need to know what you can skip first time round in the textbooks. Us the lecture, and dip in to the books as appropriate. Of course if you’re a genius, you can read the textbooks like a novel, but chances are you’ll want to focus.

If you are trying to do it without a tutor, you should find textbooks with problems and worked solutions to compare with your own. When you’re really stuck, you can ask Quora.

You can probably do the whole thing with twenty textbooks altogether, using maybe three at any one time.