This sounds good, CO2 is rarely the limiting factor in a grow anyways, you usually have to get pretty dialed before lack of CO2 starts inhibiting you. I think you should have a great start, and after you get a few runs under you belt, maybe then you could consider re-visiting CO2 if you still...
Keep an eye out for Calcium and Magnesium decifiency if you are running distilled water. One thing you could do is put a little bit of tap water in just to add a little hardness
How large is your grow? Using the air from your house will be fine for most grows.
If its a bedroom closet grow, just set your light schedule so they flower at night while you sleep, your breathing will give your plants CO2 and the plants will give you O2.
If you do draw air from outside...
I have never had 0% humidity, but its often times around 10% humidity for me. When the plants are small they seem to grow slower, however once they get larger and start drinking enough, they create their own humidity and they will speed up.