So, is QNH basically the real, actual pressure level, without temp. corrections taken into account,
Yes, but
your airfield level is indeed the level you see on your altimeter
also yes!
If you want the altimeter to read the airfield elevation when at airfield level, you don't need a temperature correction. Just take an altimeter at the airfield, set the airfield elevation and read off the subscale. That's the QNH. It's not (on a non-ISA day) the sea level pressure, but you're not interested in the sea level pressure. As long as your altimeter and the altimeter that was used to get the QNH have the same nominal pressure vs height relationship, your altimeter will read airfield elevation at airfield level with the QNH set.
If you were to set the sea level pressure on your subscale, your altimeter would assume that the pressure vs height relationship between sea level and airfield level was ISA. But if it's not (and it's usually not), the altimeter will be wrong at airfield level.