I didn't get to finish my post earlier. I was going to say that the BBB Challenge allows you to focus on volume. That's why Wendler recommended to reset the training maxes and do the minimum number of reps for the top sets because the volume work is the main focus. If you are using exactly 90% of a true max, the training sessions will definitely be challenging. Doing 5x10 for assistance at 50% won't be so bad but it'll get tough when you get to the 3rd month and have to do 50 reps of a main lift at 70% intensity.
Once you finish the 3-month Challenge, you can then begin to focus more on intensity as you begin hitting PRs in the top sets during the following months of the 5/3/1 template. After the Challenge, doing what osu122975 prescribed would be best. I actually did something similar where I did 3x8 for assistance but it looks to be a better progression if I tapered off the assistance down to 3x3 as well.
After hitting PRs and missing reps, repeat by going back to the BBB Challenge to build a foundation of volume and then transitioning into intensity. If you commit to the program, you'll see how important both volume and intensity are for building strength.