Just for 3x600W lamps you don't need so much things imho, because you have cold temperature on your side, that's a great thing.
First point: where you live? Or being specific, what kind of climate you live in? If it's cold and dry it's just perfect. If there is too much humidity then it's not perfect but it's ok...
Let's see...you don't need an intake from outdoor. Just let the air flow from the house in the growroom leaving open door or installing an extractor doing the job. Usually it contains more co2 (less o2) and it's not bad, but the most important you will avoid condensation. Any form of it, because the air is already warm. If too humid, than take in mind using a dehuey, even for a better living in the house.
Than, just place a good extractor fan of your choice blowing directly outdoor.
You can do something like this...pretty stupid but very effective. You just have to make it a little bigger.
If you can set it up this way, I think you will not have any problem with temperature, O2, CO2, condensation. But you will have issues with the smell exits outdoor, depending on the location.