As far as deloading goes...if you have a series of high intensity workouts, eventually you will put a big load on your CNS and that will negatively affect performance. So you're giving your CNS a break. Also, if you're periodizing your weights (you should be), then you will need to reset every 3-4 weeks or so. That will be a good time to deload if you need it. I can go by feel...I start to feel like shit when I get to the overreaching stage, which is what happens before you overtrain. DLs, squats, etc all put a big strain on the CNS. Even HIIT puts a big strain on the CNS...because you're going at a +90% effort.
3X5 is a good, safe rep scheme. Like Wolf said, ask DH.
For accessory lifts, I like to do 3X5-8. I typically alternate the accessory lifts about every workout. Come to think of it, I think I alternate almost all of my exercises every workout.
Check out my journal if you're interested. I'm not going to recommend my routine, but if you look at the reps & sets, then it might give you some ideas. My goal is strength. Just keep in mind that I have shitty hips and a torn up shoulder.
For every lift I do, there is a specific reason for it..and for the rep scheme. Everything from about page 53 forward might be helpful.