proper ventilation, good soil, and ample light will give you what you're looking for
so no, backyard soil will not suffice, i'd use the happy frog
the room doesn't have to be airtight , you just want to be sure the air is getting exchanged 3x a minute. so a 50 cu ft room needs 150cu /ft of air per minute, a 150 CFM fan exhausting would work, or even a fan blowing into it ghetto rigged might work on full blast
one issue i see overlooked is too much air, when plants get dried out too much, they constantly suck up water to try to regulate itself
this leads to watering more often, and the nutrients breaking down faster than the plant can use them, possibly burning them
also it can flush out whatever is in the soil that buffers the pH , such as lime.
with happy frog i will transplant a few days before flower so that way i know the soil will have enough buffering capacity until the end of the grow