1. Will these 6 exercises do anything for hypertrophy or is it strength alone? I am NOT going for powerlifter physique.. Athletic physique is what I'd like (lean mass and tight skin both in reasonable amounts).
Strength and hypetrophy will go hand-in-hand. There are no exercises that train only strength or only hypertrophy. Exercises do differ, but the effects they have a are relatively similar. After all, they are all same kind of muscle fibers. There is no such thing as a powerlifter physique. Powerlifter compete on several weight categories. There are powerlifter under 75kg and there are ones way over 120kg. You want to look lean. Many powerlifters (even over 100kg) are very lean. For the quest of getting leaner and bigger, these 6 exercises WILL give you the best results. Why? They use the most muscles, aka burn more fat. Also you work all the important and big muscles here.
Nutrition will make all the difference here. You need to eat big to get big. Simple. Bodyfat is quite simple to address via nutrition as well, you don't nececcarily need a specific program. Same goes with simple hypertrophy.
2. AxBxAxx and then rotate will HALF the # of days per week I work out. I also read that doing core work or HIIT cardio on days off is a no-no. This prospect just seems weird an feels like the breaks are giant.
It's not a no-no. It's about you and your skills to recover. Doing HIIT twice a week and 531 4 times a week didn't work for me. My quads were on too much stress and always fatiqued and sore. However, speed work once a week and HIIT once a week suit my schedule quite well.
Doing core work has the same traits as well. You work your core on every lift you do, so you don't need too much of extra core work. Doing 2-3 sets 1-3 times a week is enough. I would still recommend to have atleast one complete off-day with no hardcore exercising.
Eat right, sleep well and take care of your body. When those things are in order, you can test what's good amount of work for you.
3. Related to (2). Since I'm rolling back all the weights in order to learn proper technique AND working out seldomly, wouldn't that reverse my--modest as they are--current muscle gains?
It's a Marathon not a sprint.
There's no science that light resistance training would inhibit muscle gains. In fact, some studies say that you can get muscle volume gains with very light weights (30-50% of 1RM). Seldomly training? three times a week full-body IS NOT seldom. It's quite intense in my books. I work at this moment a body part 1-2 times a week. You work every body part three times a week. That's not seldom.
The first sentence has all there is to say. Would you rather be lifting and gaining strength and muscle for decades to come or wreck yourself with huger gains in with bad technique within the next few years? Maybe your technique work will slow down your strength gains, but they will improve you athletism (mobility, motor patterns) and health (in long term).
Besides, you'll learn quite quickly, light weight block with you won't most likely last more than a couple of weeks. After that, you work on technique on every warm up and work set, heavier and lighter intensities.
To explain why I'm concerned with hypertrophy and sufficient muscle stimulation (microtrauma?): 12 weeks ago, I was 195lb and 17.5%BF. Cleaned up my food intake and I am now 168lb and 12.5%BF. All throughout I was bodybuilding as I HATE the puny look and was going for composition change rather strict weight loss. I'm 5'10" and 28 yo.
Nutrition is the most determening part here. You lost heaps of bodyfat in a very short time. Most likely muscle as well. Cleaning the eating habits usually lower the amount of calories consumed. Want more muscle? Eat more. Eat the right nutrients at the right time. Be patient. Muscle takes more time to build than fat. You'll get your composition change.
Nothing gives you better muscle stimulation than squatting and deadlifting. NOTHING.