To answer on the only subject I've got an expertise on :
-Twice a day seem too much for me, but after all what matter is the "max recoverable volume" for each muscle groups if you want to divide these numbers into 2 workouts do as you please. But you're going to lose time, changing clothes/warm-up/unchanging clothes twice a day also.
-Frequency for muscle growth seem to be the most anabolic factor while it come to which training style you're adopting.
You can ever do more. Research nucleus-overload if you want to make 1 muscle group grow really fast.
I personally prefer the PPLPP because you've got a 2x frequency, and no training day get you tired for the next training day. I prefer it over the full-body, because I never get a nice mind-muscle connection during FB workout, but it's a matter of personal preference. But if you plan to workout 3 times a week, I'll lean toward FB
-At the end, I will balance what I said with : all of this discussion for me is some nerd bodybuilding science, and it doesn't matter. It's just about optimizing 0.5%-2% of your muscle growth. Just train in your recoverable volume (https://rpstrength.com/training-volume-landmarks-muscle-growth/), as much intensely as you can recover.
pancakemouse I've read Mike Mentzer book because I really like his physique, but I try to find evidence that his training style worked for natty, and I didn't get any, you can research on the internet about guys training like him for months for only loosing muscles. That doesn't mean you shouldn't train with intensity, but I personally lean toward more weekly volume.