So do you recommend never switching just 100% of grow use both?
All personal choice, and it won't make too much a difference overall, but enough if you want the most out of your plant.
This is how I'm doing it right now.
MH/MH from Seedling to week 4 (I veg for 2 months, every time)
MH/HPS week 4 to week 8 of veg
MH/MH or HPS/HPS Week 1-2 Depends, do you want to minimize stretch, or let them do their thing. I use MH/MH on Sativas and HPS/HPS on Indicas.
HPS/HPS Week 2-4 or 2-5
MH/HPS for the last weeks
Dual spectrum gives them the best of both worlds, and as a bonus the MH UV spectrum in flowering makes the plant produce more trichomes or bigger trichomes to protect itself from the harmful rays.
As for humidity, I personally keep it as low as possible the entire grow cycle past the first set of true leaves. Lower the humidity the more/bigger resin the plant produces.
So I would say no for a humidifier.
You can check out Advanced section, probably a lot of good threads on ways to make cannabis force more trichome growth. Just be careful, I know there is a thread on UVB lights, they cause cancer, but have been proven to work. (Cancer part is contact constantly, most people set them in the grow rooms and have a off switch outside the grow room so whenever they go to check they turn it off first to minimize risk)