Easy: whatever seems interesting.
> when, and in what order
Every single book I've read listed the things you should know before reading it in the introduction. If there's something you don't know about, you go back to the library or bookstore. Rinse and repeat, then start from the bottom and climb back up until you reach the first book. It's easy.
> and never need to ask any experienced people
There were so many experienced people on the Internet even back when I was a kid that you didn't have any problem with finding and asking them. They were incredibly helpful, especially in suggesting which books on a given topic to read. Assuming that you can get access to such people only in college is kind of elitist.
> to clear up misunderstandings
As I said, smart people are everywhere (on the Internet), just reach out and they'll help you. Well, maybe it was easier in the 90s - or maybe not, I don't know - but I'm 100% sure that not all the smart people of the world are in colleges right now.
> or have their knowledge checked
Your programs are self-evaluating proofs of your understanding. Cross-checks by others are nice, but hardly essential.
