Do not use fuel line. Get transmission cooler line and make sure it is the right size.
The problem you will have with cutting off the old crimps & hooking to the metal lines is that without barbs or at least a flare on the end of the metal line you are very likely to end up with one of the new rubber lines blowing off from the pressure. I don't care how tight you make the clamp. Odds are you will lose it and at the worst possible time (see below).
I recently had a similar kind of leak. I just ordered a new OEM set of lines and installed them. Transmissions are too expensive and the consequences of sudden fluid loss too dire for me to want to mess with it.
Air is not an issue.