Fresh Air question????

I have to move my grow room int the garage due to a new baby coming soon, here are my questions can I pull fresh air from outside ,will this invite unwanted pests and fungus? Also since im in michigan its cold in the winter so any of the FRESH air I pull is going to be cold air any solutions on this? Please somebody advise ASAP cuase Im runnin out of time and I dont want to hack this in!!!

Pull fresh air from inside the garage itself. It'll be warmer than the air outside.

Get some co2. Problem solved. Your going to have bigger issues than fresh air though. Like maintaining temps at night

Use the outside air to your advantage. Turn the fan off when the lights are off, and use the cool air to keep temps down when the lights are on. If the temps are too low even if the lights are on you may need to invest in a space heater. I have one for my bedroom. It is 1500w, but it heats up my 20x12 room so i can sleep at around 70F, there is no central air in the room. This works with the outside temp being less than 40F. Below 30F the heater struggles to keep the temp above 67F. This is a big room and the insulation is almost certainly shit. I live in a house built in the 50's. With proper insulation I bet that the heater would warm to 70F very easily. The room I am talking about has two walls sharing the outside.

You will need a good air filter for your intake air. HEPA would be good. Just saw you are in MI. If the temp is below freezing I have a hard time believing that you could warm it to a good level easily. Maybe get a thermostat controller that is connected to the intake fan for the room to make sure your room is always over 70F