At your level of strength, I don't see why you need three days of squatting, even if one is light. Your strength is high enough you will benefit from a single day since you are also deadlifting each week also. As to the DL, I would consider going light/heavy from week to week since your strength is probably about where you would start reaping the benefits of a bit more rest.
Your low back had better be bullet proof to perform RDL's twice per week, especially with all the other low back work you have. To be perfectly honest, as one who has fought low back pain for over 40 years, I wince when I read what you have laid out. Mostly because I've been in so much low back pain at times that I have vomited from the pain. Truly, I would rather see (at your strength level) you squatting once per week, DL'ing once per week until it gets heavy and either no RDL or make a decision between the RDL and a BLDL. More is not more. Too much more leads to you eventually doing something other than lifting and we all want to lift forever. Trust me, your groin will thank you eternally.
Your Press is low enough you can benefit from pounding it twice per week, one heavy one medium heavy. Your bench is low enough it would benefit from much more work, IF you are interested in a bigger bench. Over the years I've seen a bigger bench help build a bigger press, seldom the other way around.
As to assistance work. I like assistance IF I can work it in. Sometimes my overall workload is high enough that I just don't have enough left to do any justice. Other times I like to pound my assistance work just as hard as my focused movements and sometimes I hold the poundages static. It all depends on how I have set up my routine and what the focus is. Younger folks can get by with quite a bit more than older folks for a couple reasons, one is that they are obviously just young and have more energy and recovery. Other times it is simply because they are weak enough that more IS better, about the only time I'll concede that point.