"Is 4 weeks per unit not too much?"

I think 4 weeks is a good average time to spend on each unit. Some units I cut short and some I extended, but I found 4 weeks to be the right amount of time more often than not.

"Are the videos as good as the books? I feel like reading the books will take a lot of time and probably cost a lot."

The books are definitely worth reading. Many of them can be found for free at public libraries. I would read the books in your spare time though and not count it as drawing time. Also, try to apply what you learn immediately.

"Do you do the challanges/excercises during or only after you finished reading all the material?"

I would recommend doing exercises after each chapter, or even after each page in the case of dense books like Scott Robertson's.

"In retrospec, When would you have switched to digital?"

That's a tough question. I'm really glad I did so much tradition work, so I wouldn't change that. But I think I should have started doing digitial art for fun on the side about 6 months in.

"After being so dedicated would you recomment this curriculum?"

Yes, I would absolutely recommend this curriculum!