IMO, talking with someone experienced is very much worth it, even if only to understand better what to study in your situation. Or to get feedback on your exercise sheet write-ups.

Besides, I strongly recommend you find someone at your level who wants to learn these subjects as well, so you can meet regularly and discuss exercises/unclear points for free. Discussing your half-formed ideas is more fun and results in faster learning if you can unstick/learn by explaining to each other.

Some more points:

1. The core of learning math and theoretical CS is doing exercises/working with the concepts in your mind, writing down your proofs, and getting hints/corrections from time to time, rather than reading, watching, or rote-memorizing something. The idea is that, while doing that, one processes the material enough to become comfortable with it...
2. When learning a subject from the ground up, I prefer studying from lecture notes to studying a book for several reasons:
   1. They show how many "credit points" they are worth, so you roughly know how much time you'd spend on them. You can also get a better idea of the prerequisite knowledge.
   2. As mentioned by RyanCarey, studying all of a book hits diminishing returns. But making a good selection is hard to impossible - unless you are a professor preparing lecture notes.
   3. You get a better model of your knowledge after working through an entire lecture vs a part of a book. You can use this to understand what material you are ready for next, job interviews etc.

Active learning (as in brilliant.org) seems worth a try to me as well, but I don't know if it is comprehensive enough.

Usually, lecture notes are based on (and share notation with) one or a few books, which you can fall back on if you don't understand something.

I'd be happy to tutor you; I'll PM you more information about me :)