3. "If you like only doing 1 or 2 working sets, you could probably do them all twice a week. If you want to do a little more volume, you can divide this up and do half each time." -- I take that to mean that I could split them up and work out 4-days per week, hitting each exercise twice per week.
No, I was assuming that you would lift twice a week. Do something like:
Day 1: Squat, bench, row
Day 2: DL, press, chins
You said that you only have time to lift twice a week, so I assume that's still true.
Regarding failure, you probably should not be lifting to absolute failure (that's what you're doing) on a regular basis. For most of the big lifts you should feel like you still have a couple of reps left. If form breaks down (as in you have to struggle, the bar leaves it's normal path of travel, back rounds on DL or squat, etc., etc) you have gone past what is called "technical failure" and you've gone too far. There's a good old article on this subject that I can't find now, but someone will probably post the link.