Comparing x to y when y is in the executable will cause instant failure because I can pull it out and post it for everyone.  The only good way to do a licensing system is to do something involving the internet or, perhaps, generating unique numbers from a user name and an e-mail.  At worst, you need to be able to tell who the license key belonged to if someone posts it.  Being able to invalidate it is also not a bad idea.  I am aware of no open source system, but surely something exists; licensing is the kind of thing you don't open up because doing so makes it trivial to break it forever.  Also you can sell a good one for a lot of money.
As for an OS: doubt you're going to avoid assembly.  You can use brltty or something similar directly, assuming it compiles.  But you'll need a C standard library for that, and probably whatever infrastructure brltty needs to talk to the displays.  Your screen reader and your OS can be the same, especially since you're blind.  The project will be epically huge.  The best method is to learn to the point where you can get the information you need by reading the official spec and then to read the official spec.  If the official spec is confusing, you're not ready-not unless you find some books on the subject or something along those lines.  At that point, begin coding and we'll see you in a couple years or so.