I'm not sure that those questions can be answered specifically. I think what is important to ask you is what type of tank you are using? Is it a MTL (mouth to lung) or DTL (direct lung) tank?
I believe all of the SMOK
tanks are sub-ohm DTL, so they are designed to have maximum air draw and maximum vapor production. They are known more for being cloud chasing tanks, not so much for flavor makers. I don't believe anyone can say you should have airflow at 25% or 50% or 100%. That is a personal preference that only you can decide upon.
The same holds true for wattage setting. The recommended wattage setting for any particular coil used is usually imprinted on the coil or in the user's manual, but that is merely a recommendation and is not written in stone. Experiment through trial and error, with different wattage settings on the mod and different airflow adjustments on the tank to see what YOU prefer.
I would guess, in general, that the lower the ohms of the coils and the higher the wattage set, the more wide open the air control should be. But that's just my guess.
Over the years, I have found that "my sweet spot" is 30 watts, usually with a 0.5 ohm coil. I play around with the air control on the tanks that I use, depending upon my mood and what type of draw I want at any particular time. I converted from being a low wattage MTL vaper a few years ago to a mid-range wattage DTL vaper. That's not to say that you would like that.
We all learn through trial and error to find what works best for us. Maybe that doesn't help answer your queston, but maybe it does.