I've heard some criticism about Caroll's style and about the book, while I've also heard praise. What side is more "correct" than the other? Is Liber Null truly a good book for a beginner?
It's not the first book I would read, But yes, it is a good book for beginners. One of the better actually.
People who complain about Carrol are usually traditional magicians who simply don't agree with his methods at all. It's like muslims complaining about christian. It's the same religion, they just have different methods of interpretation, and some have added something that others haven't added. And then they start argue over details and the negative shit never ends.
Don't worry about what others say.
Do I move on to breath control once I achieve 15 minutes again?
You can move on, or you can just add it upon your current practice.
I recommend still incorporating it some. There are Buddhist monks that spends years doing nothing but breath control.
When I get to not-thinking, how much should I expect to achieve before moving on to concentration?
How will you know the time if you are not thinking....
When I get to concentration training, what schedule should I follow? Which training goes first and for how long?
Easiest stuff first, harder stuff later.
Keep going till you feel like it's good enough.
If you go to the gym, should you lift 8 times or 10? Well that depends on how much you can do.
If you fell like 5 minutes is exhausting then do 5 minutes. if you feel like nothing really happens before you do it for at least 30 minutes. do that.
Should I keep a dream diary right now?
Keep doing your dream journal for at least a year.
Most keep doing it the rest of their lives.
When do I start doing rituals and sigils? When I get to Liber Lux, or once I'm done with concentration training?
When you know that you are ready.
Not when you feel that you are ready, or think that you are ready, When you know.
