Stretch reflex on overhead press, yes or no?

I do my OP in the "military press" style. I perform each rep from a dead stop, resting on my breastbone and extending my arms quickly and nearly locking out the elbows before slowly bringing it back to my chest. Inhale & repeat.

I was taught that it should be a brute force exercise and not one that uses momentum, you should "muscle it up".

Really depends on your goals. I only pause on exercises where I set the weights on the floor.

I don't, I pause on each rep to steady my stance. I have really poor balance though so it's probably a necessity to me.

Ya I started with SL 3 months ago as a total beginner to see if I could gain some strength. (And it's worked of course.) I didn't expect to fall in love with moving heavy things along a vertical path. I figure if I'm going to lift for fun I might as well add some muscle mass while I'm at it.

About the 3X8, my understanding is that the reps per set is what determines more whether the result will be strength vs hypertrophy. How many sets should I be doing if I'm doing 8 reps per set?

I tend to think the folks that do the best with building muscle mass are the ones that lift for both strength and hypertrophy. Building strength increases the magnitude of the tension you place on your muscles, and building mass ups your potential strength ceiling. They really go hand in hand in my opinion.

Anyhow, reps per set is part of the equation, but what really causes hypertrophy is recovering from those microtears you create when you lift weights. That's why adequate nutrition and sleep on such a program is so important. Anywho, you need to maximize time under tension on the body parts you're hitting (that's why you'll see bodybuilders do what seems to be half reps on bench and stuff, it's not laziness but rather because the top half of the bench is more triceps and takes tension off the chest. Part of that is keeping the muscles activated for longer (i.e. upping the reps per set and keeping the muscles activated throughout the set) but that doesn't mean you should reduce the total workload. Quite the opposite in fact, powerlifters can get away with far less total work than bodybuilders.

If you like StrongLifts, I'd say stick with that rotation for your primary lifts, and work on increasing your strength ceiling with those. I'd still focus on time under tension, so touch and go for the lifts (NOT BOUNCE) rather than pausing your reps, but really focus on strength progression. Then when you're finished with your StrongLifts session, add in accessory work that really focuses on hypertrophy. A lot of the specifics of accessory work are dependent on what you want to do, but make sure you hit your whole body and include some prehab/rehab stuff as well.