From Surovetsky's own mouth:
-You can do lat work whenever you want.
-Keep triceps assistance on heavy benching days.
-Other upper body work can be done on any day (e.g., biceps work, different delt raises).
-Do whatever lower body, lower back work you need, just be mindful of the effect it will have on your next session. This will take some experimenting on your part.
-Avoid doing too much assistance with a barbell.
-Keep assistance in the 3-4x6-10 range, leave a couple reps in the tank.
-Surovetsky is adamant that assistance is a very individual matter, and specific advice can't really be given without working with somebody. I.e., you're going to have to play around and see what works. Don't be afraid to add 2-3 bodybuilding type movements to the end of every session, just don't push these to failure and you should be fine.
-I train on these systems and find that more than anything, it is time that limits me from doing more assistance. Doing 3 sets of delt raises and 3 sets of pulldowns is not going to take that much out of you, but after squatting and benching for 2.5 hours, I often just do not have time to spend on it.
I also notice you're indicating you will lift three days. One thing that Surovetsky advises, that I have done successfully, is split the heavy days each week, so train four days, e.g., Squat/Bench medium, Bench/Deadlift light, Bench heavy, Squat heavy. This leaves a little more room/time for assistance on the heavy days. If you're committed to three days that's certainly not a problem though.
Bottom line is you have a lot of room to play around with different assistance schemes when training this way. I'd start bare bones and build your assistance work out as needed.