Running big pots isn't an issue AS LONG AS you have good watering practices.
Big pots are tough to get uniform dry back, that's one of the reasons to step up pot sizes.
Doing stepped up-sizing also allows the exterior root growth of the smaller pot to develop in the fresh media rather than relying on a tap root to fill a big tub.
On the 2nd question-on my last pheno hunt of some Primal Punch, I had to super-crop a large girl to maintain canopy height as it stretched during the 1st week of flower.
That girl popped a few nanners because of the stress.
I'm currently running the same pheno in my main grow(it's that remarkable) and at 30 days in flower, they are stunning.
So, I'd be hesitant to do any serious manipulation especially when the plants are charged with flowering hormones during stretch.