Back off sets are for practicing form.
When your bench press gets stuck, Rip recommends adding chinups/pullups first. Dips will probably help, but you'll hear mixed opinions on this from members of these forums (I asked a while ago). Close grip benches and rack lockouts aren't necessary for novices.
For your squat question, it depends on the situation. Assuming that nutrition and sleep are accounted for as you said, if you're making 10 lb jumps and your squats are getting exceedingly difficult, you switch to making 5 lb jumps. If you're making 5 lb jumps and your squats are getting exceedingly difficult, you switch to the advanced novice program, which has you squatting heavy twice per week with a light squat day programmed in the middle of the week (still increasing by 5 lbs on the heavy squat days).
If you think your abdominals are weak and are causing your lifts to stall, then adding heavy ab work would be beneficial.
I had typed up an answer to the rest of your question, but I realized that I didn't feel comfortable providing the information for it based on my experience level. Maybe someone who is more knowledgeable than I am can help out.