Well, if your goal is what they more or less advertise in the program, why not just pretty much do that for a bit if you are not real experienced on those big lifts? Later on, after you put in some time a d learn your weaknesses, you might know better what assistance work you would benefit from more? That way most, or all your attention would go into working hard and drilling just a handful of exercises you would get stronger at, instead of trying to learn or save energy for less benefiting stuff IMO?
Remember, assistance work is not magic (especially for trainees not real advanced) the main exercises are just that, main gainers. And more exercises, will never trump hard work on a handful of the multi joint spine loading compounds.