I can't address your questions directly, but perhaps you find this interesting; I read this book recently: https://www.amazon.co.uk/Cannabis-seeing-through-smoke-Science/dp/1529360498
It's written by a British professor who has quite some experience in the field of marijuana (and psychedelics), I can recommend it to anyone interested in reading up on impacts on health of smoking marijuana and (to a limited extend) the combination of THC and CBD in marijuana strains.
According to the book, most of the research that has been done on the effects of marijuana on health have been on strains containing <12% THC and up to 4% CBD. Much of this research concludes a limited negative impact on health and even positive impact in some cases, and if I remember correctly most of the positive impact come from the combination of CBD and THC. Though many of the strains today contain materially more THC (up to ~24%) with negligible amounts of CBD, which seem to introduce/increase potential negative impacts (though not much research has been done on these high THC low CBD strains).
I'm sharing this because after reading the book I decided to switch to strains with lower THC and relatively more CBD to avoid any negative impact (as I've been smoking quite some bit during the pandemic). As it's hard to find strains containing CBD and low THC in my area I decided to take CBD drops while smoking. I haven't directly noticed a huge difference, but this was more due to the poor/inconsistent quality of marijuana available to me - which is why I've started growing myself. The book led me to decide to focus on strains with max ~12% THC and at least some CBD as to limit any potential negative impact.