New to program

I am not exactly brand new to weightlifting. I've been doing CrossFit and weight training for over 10 years.
Where should I start weight wise with this program? not 45 lbs I would assume?
And what happens when you plateau at a weight? As in not able to finish all five reps?
Do you just lower the reps the next workout or go down in weightt or how does that work??

I would suggest, buying the book.