Maybe not as much of a concern. It's likely the car needs to warm up for a few minutes when starting, so you don't want to do that idling inside. Easy enough to just drive in and immediately shut it off though.
You'd still end up pumping quite a lot of carbon monoxide into your living space doing that, I think.
It wouldn't be significant - leave the garage door open for a few minutes and you would be fine. I imagine he has ventilation designed to take this into consideration.
Would you need to do at at all? As it wouldn't get cold.
Cold for an engine block and timing belts and cold for a person are two different things